Please help me find the equation (number form) to this!

Question

Two angles in a triangle have the relationship such that the first angle is six less than seven times the measure of the third angle. If the two angles have a sum of 90 degrees, find the measure of both angles.

Answer 1

A₁ = 7A₃-6

A₁+A₃=90

Substitute from equation 1 into equation 2

7A₃-6+A₃=90

8A₃=96

You solve it from here.