Solve the Problem $\mathrm { M } ( \mathrm { x } )$

Multiple Choice

Solve the problem.
-The number of mosquitoes $\mathrm { M } ( \mathrm { x } )$ , in millions, in a certain area depends on the June rainfall $\mathrm { x }$ , in inches: $\mathrm { M } ( \mathrm { x } ) = 13 \mathrm { x } - \mathrm { x } ^ { 2 }$ . What rainfall produces the maximum number of mosquitoes?

A) 0 in.
B) $169 \mathrm { in }$ .
C) $6.5 \mathrm { in }$ .
D) 13 in.