21-3 Using the high-low method Martin owns a machine shop. In reviewing the shop's utility bills for the past 12 months, he found that the highest bill of $2,800 occurred in August when the t chines worked 1,400 machine hours. The lowest utility bill of $2,600 occurred December when the machines worked 900 machine hours. Requirements 1. Calculate the variable rate per machine hour and the total fixed utility cost 2. Show the equation for determining the total utility cost for the machine s 3. If Martin anticipates using 1,200 machine hours in January, predict the sh total utility bill using the equation from Requirement 2