Larker brothers, inc., 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: 3,000 machine hours3,200 machine hours3,100 machine hours2,900 machine hours