Answer
C; $22ft/s$
Work Step by Step
Use a conversion table to convert miles per hour into feet per second.
$\frac{15mph}{}$|$\frac{5280ft/hr}{1mph}$|$\frac{1ft/s}{3600ft/hr}$
Multiplying across the top and bottom gives us $\frac{79200}{3600}ft/s$, which reduces to $22ft/s$
