Given: Lines y and z are parallel, and ABC forms a triangle.
Prove: m25+ m22 + m26 = 180° which could be the missing reason in step 3

This problem has missing information, so I've provided my own diagram below.

By Alternate Interior Angles:

Angles ∠6 and 48 degrees are supplementary:

Internal angles of every triangle add up to 180 degrees:

Finally:

step-by-step explanation:

step 1: solve one of the equations for one of the variables. let's solve the first equation for y:

step 2: substitute that equation into the other equation, and solve for x.

step 3: substitute x = 4 x = 4 x=4 into one of the original equations, and solve for y.