A = 157, B = 23
The definition of supplementary angles is that they add up to 180 degrees. So A+B = 180. And A = 7B - 4.
So write down the formula
A + B = 180
Substitute the formula for A in terms of B
7B - 4 + B = 180
Combine terms
8B - 4 = 180
Add 4 to both sides
8B = 184
Divide both sides by 8
B = 23
Now calculate A in terms of B
A = 7B - 4
A = 7 * 23 - 4 = 161 - 4 = 157
Verify that A and B add up to 180
157 + 23 = 180
