Alexander, J. Worswick, C.j., and Morgan, J., concur.
Clyde Parrish, Sr., appeals an order of the Pierce County Superior Court granting a summary judgment in favor of the McChord Credit Union and against him as a guarantor of a debt his son, Clyde Parrish, Jr., owed on a promissory note after credit was given for the proceeds received by McChord from the sale of the collateral. Clyde, Sr., argues on appeal that McChord was not entitled to a deficiency judgment because (1) McChord did not provide statutory notice to him or the principal debtor, Clyde, Jr., of its disposition of the collateral; (2) the sale of the collateral was not commercially reasonable; and (3) McChord, having agreed to Clyde, Jr.'s sale of the collateral to a third party, is estopped from enforcing the guaranty. We modify the judgment.
On February 8, 1985, Clyde Parrish, Jr., obtained a loan from the McChord Credit Union in order to purchase an automobile, a 1985 Honda Accord. The debt owing McChord, $10,014, was guaranteed by Clyde, Sr.*fn1 Clyde, Jr., made the required monthly payments of $222.75 until October 1986, when he sold the car to Stephanie Irons. Clyde, Jr., asserts on appeal, as he did in the trial court,
that he sold the car with the approval of McChord.*fn2 Irons made the monthly payments to McChord until April 1988, when she ceased payment.
On January 5, 1989, McChord filed an action in Pierce County Superior Court for the entire balance due on the note. McChord named as defendants Clyde, Jr., and his wife; Clyde, Sr., and his wife; and Stephanie Irons and her husband.
On January 20, 1989, McChord took possession of the Honda automobile. Sometime later, it advertised the car for sale in the Pierce County Credit Union's newsletter and on signs posted in the credit union lobby. McChord sold the car on March 20, 1989, for $3,500. Neither of the Parrishes received notice of the sale until May 1989. Clyde, Sr., acknowledges, however, that he was aware that McChord had possession of the car in April of 1989.
McChord moved for summary judgment, claiming that as a guarantor of the loan, Clyde, Sr., was liable for the balance due on the note. The motion was granted.
 The question before us is whether the trial court erred in granting summary judgment to McChord. Summary judgment should be granted only where there is no dispute as to any material fact and the moving party is entitled to judgment as a matter of law. CR 56(c). In ruling on the motion, the trial court must view the evidence in the light most favorable to the nonmoving party. If reasonable minds could reach different conclusions on the evidence, the motion for summary judgment must be denied. Jacobsen v. State, 89 Wash. 2d 104, 569 P.2d 1152 (1977). We engage in the same inquiry as the trial court, on the same record. Wilson v. Steinbach, 98 Wash. 2d 434, 656 P.2d 1030 (1982).
Clyde, Sr., contends that he and his son were both entitled to proper notification of McChord's sale of the car. He claims that McChord's failure to provide such notice violates the Uniform Commercial Code and precludes McChord from recovering a deficiency judgment. Clyde, Sr.'s contention requires us initially to answer two questions: Was he entitled to notice and, if so, did he receive such notice?
 In order to recover, a creditor must make a commercially reasonable disposition of the collateral. RCW 62A.9-504(3). The creditor has the burden of proving commercial reasonableness, Rotta v. Early Indus. Corp., 47 Wash. App. 21, 24-25, 733 P.2d 576, review denied, 109 Wash. 2d 1012 (1987), and reasonableness is a question of fact for the trier of fact. Service Chevrolet, Inc. v. Sparks, 99 Wash. 2d 199, 204-05, 660 P.2d 760 (1983). One ingredient of commercial reasonableness is sufficient notice both to the debtor and to the public at large. Rotta, 47 Wash. App. at 25. RCW 62A.9-504(3) explicitly addresses this:
[R]easonable notification of the time and place of any public sale or reasonable notification of the time after which any private sale or other intended disposition is to be made shall be ...