### Solution

From the figure, we can see that the measure of $∠A$ is $70_{∘}$ and that the measure of $∠B$ is $3x+7_{∘}.$ Since the measures are equal, we can write an equation.
$70_{∘}=3x+7_{∘} $
We will now solve the equation by using inverse operations.

$70_{∘}=3x+7_{∘}$

SubEqn$LHS−7_{∘}=RHS−7_{∘}$

$63_{∘}=3x$

RearrangeEqnRearrange equation

$3x=63_{∘}$

DivEqn$LHS/3=RHS/3$

$x=21_{∘}$

### Hint

Equate the measures of $∠A$ and $∠B.$

### Answer

$x=21_{∘}$