Answer
$\approx 67,000 \text{ miles per hour}$
Work Step by Step
From part (b), the angular speed is $\dfrac{\pi}{4380}\text{ radians per hour}$
Thus, to find the linear speed of Earth in miles per hour, use the formula $v=r\omega$ to obtain:
\begin{align*}
v&=93,000,000\left(\frac{\pi}{4380}\right)\\\\
v&\approx67,000\text{ mph}
\end{align*}