Stuck on a word problem, precalc 110

Question

Craig builds luxury bird houses And he sells them at weekend craft fairs. If he charges 30$ each he can sell 20 of them in a weekend, but he predicts for every 2$ decrease in price he will sell 4 more houses

A) write the quadratic function to model this solution

B) what price should Craig charge in order to sell the most houses?

 

C)how many houses can he expect to sell at that price?

 

D)how much revenue can he expect at that price??

Answer 1

d represents the number of deceases

f(d) = (30 - 2d)(20 + 4d)

Convert to vertex form to determine value of d that provides the maximum.