#### Answer

$-756^{\circ}$

#### Work Step by Step

In order to convert a radian measure to degrees, we must multiply the given radian measure by $\frac{180}{\pi}^{\circ}$ and simplify.
Therefore, $-\frac{21\pi}{5}radians=-\frac{21\pi}{5}(\frac{180}{\pi}^{\circ})=-\frac{3780\pi}{5\pi}^{\circ}=-756^{\circ}$.