Lamar Corporation's purchasing manager obtained a special price on an aluminum alloy from a new supplier, resulting in a direct-material price variance of $9,500F. The alloy produced more waste than normal, as evidenced by a direct-material quantity variance of $2,000U, and was also difficult to use. This slowed worker efficiency, generating a $2,500U labor efficiency variance. To help remedy the situation, the production manager used senior line employees, which gave rise to a $900U labor rate variance. If overall product quality did not suffer, what variance amount is best used in judging the appropriateness of the purchasing manager's decision to acquire substandard material