By Cosine Law
$30^2 = 20^2 + 40^2 - 2(20)(40) \cos \alpha$
$2(20)(40) \cos \alpha = 20^2 + 40^2 - 30^2$
$1600 \cos \alpha = 1100$
$\cos \alpha = 0.6875$
$\alpha = 46.57^\circ$ answer
$20^2 = 30^2 + 40^2 - 2(30)(40) \cos \theta$
$2(30)(40) \cos \theta = 30^2 + 40^2 - 20^2$
$2400 \cos \theta = 2100$
$\cos \theta = 0.875$
$\theta = 28.96^\circ$ answer