Answer
$C=60^\circ$
$b \approx11.52$,
$c \approx10.13$
Work Step by Step
1. Find the third angle $C=180-100-20=60^\circ$
2. Use the Law of Sines $\frac{4}{sin20^\circ}=\frac{b}{sin100^\circ}=\frac{c}{sin60^\circ}$
3. $b=\frac{4sin100^\circ}{sin20^\circ}\approx11.52$,
$c=\frac{4sin100^\circ}{sin60^\circ}\approx10.13$
