8 Question 9 Question 10 Question 11 Question 12 Question content area top Part 1 Test Laboratories does heat testing (HT) and stress testing (ST) on materials. Under its current costing system, aggregates all operating costs of into a single overhead cost pool. calculates a rate per test-hour of ( / total test-hours). HT uses test-hours, and ST uses test-hours. Gary , 's controller, believes that there is enough variation in