Cox Engineering performs cement core tests in its laboratory. The following standards have been set for each core test performed: 4 Standard Hours or Quantity Standard Price or Rate Direct materials 3.0 pounds 80.75 per pound Direct labour 0 4 hours $12 00 per hour Variable manufacturing overhead 0 4 hours 19.00 per hour During March, the laboratory performed 2,000 core tests. On March 1 no direct materials (sand) were on hand. Variable manufacturing overhead is assigned to core tests on the basis of direct labour hours. 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 labour hours were worked at a cost of $8,610. Actual variable manufacturing overhead incurred was $3,200. The variable manufacturing overhead efficiency variance for March is: