Find the Slope of the Curve at the Indicated Point $\mathrm { P }$

Find the slope of the curve at the indicated point.
-The power $\mathrm { P }$ (in $\mathrm { W }$ ) generated by a particular windmill is given by $\mathrm { P } = 0.015 \mathrm {~V} ^ { 3 }$ where $\mathrm { V }$ is the velocity of the wind (in mph) . Find the instantaneous rate of change of power with respect to velocity when the velocity is $9.0 \mathrm { mph }$ .

A) 8.1 W/mph
B) 3.6 W/mph
C) 0.4 W/mph
D) 21.9 W/mph