Angle sum theorem
for
x​

“exterior angles of triangles. an exterior (or external) angle is the angle between one side of a triangle and the extension of an adjacent side. try this drag the orange dots on any vertex to reshape the triangle.” look to get to the answer i explained what it means and other things i hope it you .

The answer will be y=-5+0 because the slope is -5 and the it has to go through y-axis 0