Answer
$897.84$mph.
Work Step by Step
We know that $d=2r\pi=2(3429.5)\pi=6859\pi$ miles.
We also know that $\text{linear speed}=\frac{\text{distance}}{\text{time}}$ and that $1$ day consists of $24$ hours. Hence $\text{linear speed}=\frac{6859\pi}{24}\approx897.84$mph.