McRobert's Electronics sells 200 TVs per month at a price of $400 per unit. Market research indicates

Question:

McRobert's Electronics sells 200 TVs per month at a price of $400 per unit. Market research indicates that the store can sell one additional TV for each $1 it reduces the price. In this case the total revenue is
R(x) = (200 + x) (400 - x)
where x is the number of additional TVs beyond the 200. If the store sells a total of 250 TVs, find the marginal revenue. Interpret your result.