At an activity level of 5,000 machine-hours in a month, total variable production engineering cost is $55,000 and its total fixed production engineering cost is $12,500. What would be the total production engineering cost per unit, both fixed and variable, at an activity level of 5,600 machine-hours in a month? Assume that this level of activity is within the relevant range. O a. $12.32 O b. $13.23 O c. $12.05 O d. $13.5