Testing 1-2-3 is a microphone testing company that performs several tests and analyses for any type of equipment that has a microphone (e g smartphones, laptops, public address systems, etc) Three of the tests that they perform require the use of a specialized machine that can operate for 14,000 hours per year Information on the three equipment tests, separately and as a combined full-service package, follows: Test 1Test 2 Test 3 Test 4 (AIl) $48 $164 Charging rate Variable cost Machine hours $6 $51 S1 What is the contribution margin per hour of machine time for Test A Select one a $15.67 b $65 C. $40 d $13.33 e s25.50