Chapter 3 - Radian Measure and the Unit Circle - Section 3.4 Linear and Angular Speed - 3.4 Exercises - Page 125: 39c

$\approx 67,000 \text{ miles per hour}$

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*}