Answer:
[tex]\huge\boxed{m\angle B=30^o}[/tex]
Step-by-step explanation:
[tex]\text{We know:}\\\text{The angles in each triangles add up to 180}^o.\\\\\text{Therefore we have:}\\\\m\angle A+m\angle B+m\angle C=180^o\\\\\text{Substitute}\ m\angle A=2x,\ m\angle B=x,\ m\angle C=3x:\\\\2x+x+3x=180\qquad\text{combine like terms}\\\\6x=180\qquad\text{divide both sides by 6}\\\\\dfrac{6x}{6}=\dfrac{180}{6}\\\\x=30\\\\m\angle B=x\to m\angle B=30^o[/tex]
