Answer
$m\angle A=120$
$m\angle B=60$
Work Step by Step
It is given that $m\angle A=2m\angle B$.
$m\angle A+m\angle B=180\longrightarrow$ definition of supplementary
$2m\angle B+m\angle B=180\longrightarrow$ substitution
$3m\angle B=180\longrightarrow$ combine like terms
$m\angle B=60\longrightarrow$ division property of equality
Substitute to find $m\angle A$.
$m\angle A=2m\angle B=2(60)=120$
