With 4,000 machine-hours in a month as an activity level, Brant Corporation's total variable production engineering cost is $154,200 and its total fixed production engineering cost is $129,000. What would be the total production engineering cost per unit, both fixed and variable, at an activity level of 4,300 machine-hours in a month? Assume that this level of activity is within the relevant range.
a. $68.33
b. $68.55
c. $70.80
d. $65.86