If the price is p and the quantity of bread sold is q = 400 - 100p, the average collection, in reais, depending on the price p, is given by R (p) = (400 - 100p). P
For this collection to be R $ 300.00, you must have:
(400 - 100p). p = 300 ⇔ 4p - p² = 3 ⇔ p² - 4p + 3 = 0 ⇔ p = 1 or p = 3
R $ 300.00
The current price is R $ 3.00, as R $ 300,000 / 100 = R $ 3
To maintain the collection, the price must be lowered to R $ 1.00 (R $ 0.50 <R $ 1.00 <R $ 1.50)
ANSWER: letter A