Question

solve for x. find m∠y

Explanation:

Step1: Use vertical - angle property

Vertical angles are equal. So, $3x - 1=15x - 17$.

Step2: Solve the equation for $x$

Subtract $3x$ from both sides: $-1 = 15x-3x - 17$, which simplifies to $-1=12x - 17$.
Add 17 to both sides: $16 = 12x$.
Divide both sides by 12: $x=\frac{16}{12}=\frac{4}{3}$.

Step3: Find the measure of an angle related to $\angle y$

The angle adjacent to the $129^{\circ}$ angle (let's call it $\angle z$) has a measure of $180 - 129=51^{\circ}$ (linear - pair of angles).
$\angle y$ and the $51^{\circ}$ angle are vertical angles.

Answer:

$m\angle y = 51^{\circ}$