Cox Engineering performs cement core tests in its laboratory. The following standards have been set for each core test performed: Direct materials, 3 pounds @ $0.75 per pound. Direct labor, 0.4 hours @ $12.00 per hour. Variable factory overhead, 0.4 hours @ $4.00 per hour. Fixed factory overhead, 0.4 hours @ $10.00 per hour. Manufacturing overhead is assigned to core tests on the basis of direct labor hours. Budgeted fixed manufacturing overhead for the period was $8,000. The denominator activity used for determining the overhead rates was 2,000 core tests or 800 direct labor hours. On March 1 no direct materials (sand) were on hand. The following events occurred during March: 8,600 pounds of sand were purchased at a cost of $7,310. 7,200 pounds of sand were used for core tests. 840 actual direct labor hours were worked at a cost of $8,610. Actual variable manufacturing overhead incurred was $3,200. Actual fixed manufacturing overhead incurred was $8,100. The company actually performed 2,000 core tests during the month.

The variable overhead rate variance for March is: A) $320 unfavorable. B) $320 favorable. C) $160 unfavorable. D) $160 favorable.

The variable overhead efficiency variance for March is: A) $320 unfavorable. B) $320 favorable. C) $160 unfavorable. D) $160 favorable.

I know the answer for the first question is D. 160 unfavorable and the answer to the second one is C.160 unfavorable but I need to know how to get to those answers. Please explain step by step the formula you use and how you got the numbers you used in the formula.