At an activity level of 4,000 machine-hours in a month, Curt 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) $65.86 D) $70.80