The standard costs and actual costs for direct materials for the manufacture of 2,140 actual units of product are as follows: Direct materials Standard Costs 2,140 kilograms at $8.50 Actual Costs Direct materials 2,200 kilograms at $8.00 The direct materials quantity variance is Oa. $510 favorable Ob. $408 favorable Oc. $408 unfavorable Od. $510 unfavorable