Agrocer sells 30 loaves of bread a day. the cost is $2.50 per loaf. the grocer estimates that for each $0.50 increase in cost, 2 fewer loaves of bread will be sold per day. let x represent the number of $0.50 increases in the cost of a loaf of bread.

If x is the number of $0.50 increases, then the cost of a loaf of bread will be (2.5 + 0.5x) then the number of loaves sold per day will be (30 - 2x).
Then the revenue will be the product of the cost and the number of loaves:
Revenue = (2.5 + 0.5x)(30 - 2x) = 75 + 10x - x^2
If we want to maximize revenue, we take its derivative and equate to 0:
d(Revenue)/dx = 10 - 2x = 0
x = 5
So to maximize revenue, x = 5, which corresponds to a price of (2.5 + 0.5x) = $5/loaf. This will correspond to sale of (30 - 2x) = 20 loaves. The total revenue will be ($5/loaf)*(20 loaves) = $100.