Rate Conversions: ft/s, mph and km/h

The one factor worth memorising: $60$ mph is exactly $88$ ft/s. Everything follows from the ratio $\frac{88}{60} = \frac{22}{15}$.

So mph $\to$ ft/s multiplies by $\frac{22}{15}$, and ft/s $\to$ mph multiplies by $\frac{15}{22}$. For example $440$ ft/s $\times \frac{15}{22} = 300$ mph.

Look for multiples of $22$ in ft/s and multiples of $15$ in mph — the problems are built so one of them cancels cleanly.