Solve the Problem $P ( x ) = - x ^ { 2 } + 56 x + 71$

Multiple Choice

Solve the problem.
-John owns a hot dog stand. He has found that his profit is represented by the equation $P ( x ) = - x ^ { 2 } + 56 x + 71$ , with $P$ being profits and $x$ the number of hot dogs sold. How many hot dogs must he sell to earn the most profit?

A) 43 hot dogs
B) 21 hot dogs
C) 29 hot dogs
D) 28 hot dogs