Let "AQ" = actual quantity of direct materials issued to production. AP = actual price paid per unit of direct material purchased, SP = standard price per unit of direct material, and SP = standard quantity of direct materials allowed based on actual output for the period. Use the above notation to develop a formula (Le., an equation) for each of the following standard cost variances: 1. Direct materials price variance (calculated at point of production, not point of purchase). 2. Direct materials usage variance. 3. Flexible-budget (FB) variance for direct materials. 4. Joint price-quantity variance for direct materials