We can find the answer to this by using the equation for finding marginal revenue. This equation is
marginal revenue = change in total revenue/change in quantity.
In this case, the original total revenue is found by multiplying the 14 units made by the $32 charged for each unit. 14*32 = $448. The new total revenue is found by multiplying the 15 units made by the $31 charged for each unit. 15*31 = $465 To find the marginal revenue, we calculate $465 - $448 and get $17. Since the change in quantity is 1, marginal revenue is $17.
The marginal revenue received by the monopolist for the 15th unit is $17.