AHSME 1995 Problem 7

The radius of Earth at the equator is approximately 4000 miles. Suppose a jet flies once around Earth at a speed of 500 miles per hour relative to Earth. If the flight path is a neglibile height above the equator, then, among the following choices, the best estimate of the number of hours of flight is:

$\mathrm{(A) \ 8 } \mathrm{(B) \ 25 } \mathrm{(C) \ 50 } \mathrm{(D) \ 75 } \mathrm{(E) \ 100 }$