#### Answer

$5.16~km/s$

#### Work Step by Step

The required speed can be determined as follows:
$v_{\circ}=\sqrt{\frac{GM_e}{r{\circ}}}$
We plug in the known values to obtain:
$v_{\circ}=\sqrt{\frac{66.73\times 10^{-12}\times 5.976\times 10^{24}}{15\times 10^6}}$
This simplifies to:
$v_{\circ}=5156m/s=5.16~km/s$