Answer:
$25,340
Explanation:
Considering that the statement indicates that the average cost of painting 20 houses is $1,200 per house and that the marginal cost that is the additional cost to produce another unit is $140, you can calculate the cost of painting 21 houses by doing the following:
($1,200*20)+($1,200+$140)= $24,000+$1,340= $25,340
The total cost of painting 21 houses is $25,340.