Answer:
c
Explanation:
To find the maximum point, differentiate:
D' = -8p +160
Set to zero and solve for p:
D' = 0
⇒ -8p +160 = 0
⇒ 8p = 160
⇒ p = 20
Input p = 20 into the original equation to find D:
D = -4(20)² + 160(20) -310 = 1290
Therefore, the price is $20 and the maximum number of drills is 1,290