10. Larker Brothers, Incorporated, used the high-low method to derive its cost formula for electrical power cost. According to the cost formula, the variable cost per unit of activity is $4 per machine- hour. Total electrical power cost at the high level of activity was $19,200 and at the low level of activity was $18,400. If the high level of activity was 3,300 machine hours, then the low level of activity was: a. 3,100 machine hours b. 3,200 machine hours c. 3,000 machine hours d. 2,900 machine hours