Answer
$\theta_3 = 0.02325~rad$
$\theta_3 = 1.33^{\circ}$
Work Step by Step
We can write an expression when there is double slit interference:
$d~sin~\theta_m = m~\lambda$
We can find the angle in radians when $m = 3$:
$d~sin~\theta_m = m~\lambda$
$sin~\theta_m = \frac{m~\lambda}{d}$
$sin~\theta_3 = \frac{(3)~(0.620~\mu m)}{80~\mu m}$
$sin~\theta_3 = 0.02325$
$\theta_3 = sin^{-1}~(0.02325)$
$\theta_3 = 0.02325~rad$
We can convert this angle to degrees:
$\theta_3 = (0.02325~rad)(\frac{180^{\circ}}{\pi~rad})$
$\theta_3 = 1.33^{\circ}$
