Question

find m∠1
m∠1 = □
(type an integer or a fraction. do not include the degree symbol in your answer)

Explanation:

Step1: Use vertical - angle property

Vertical angles are equal. So, $3x + 5=123$.

Step2: Solve for $x$

Subtract 5 from both sides: $3x=123 - 5=118$. Then $x=\frac{118}{3}$.

Step3: Find $\angle1$

Since $\angle1$ and the angle marked $123^{\circ}$ are vertical angles, $\angle1 = 123$.

Answer:

123