(iii) Average maintenance costs are $1.50 per machine hour at an activity level of 8,000 machine hours and $1.20 per machine hour at an activity level of 13,000 machine hours. Assuming that this activity is within the relevant range, total expected maintenance cost for a budgeted activity level of 10,000 machine hours would be closest to which of the following? a) $11,433 b) $15,000 c) $13,440 d) $16,128 e) $13,143