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Ruby Company peoduces a chair for which the standard specifies 4 yards of material per unit. The standard price of ane yard of material is 3a, 40 . During the month. 6,400 chairs were manufactured, using 25,100 yards at a cost of $7.98 per yard. Determine the following: Enter favorable variances as negative numbers. a. Ditect materials price variance b. Direct materiais quantity variance c. Total direct materials cost variance