The property demonstrated is co-interior, which states that two angles like the one shown is equal to 180 degrees.
You can then make this formula.
180 = (5x + 13) + (3x - 5)
Now solve this formula
180 = 5x + 13 + 3x - 5
180 = 8x + 8
172 = 8x
/8 /8
21.5 = x
Proof that x = 21.5
5(21.5) + 13 = 107.5 + 13 = 120.5
3(21.5) - 5 = 64.5 - 5 = 59.5
59.5 + 120.5 = 180 degrees.
