4. A stereo company sells 300 car stereos per month at a price of $280 per car stereo. Market research indicates that they can sell one additional stereo for each $1 they reduce the price. Find the marginal revenue for the stereo company. a) -10 - I b) 10 + C) -10 + 1 -20 21 20 + 20 e) Bo brak Knceki 4/10 Sonraki> Kapat Snav Bitir