Take into account that angle 9x+7 and 115 are congruent because they are alternate exterior angles.
Then, you can write:
9x + 7 = 115
Solve the previous equation as follow:
9x + 7 = 115 subtract 7 both sides and simplify
9x = 115 - 7
9x = 108 divide by 9 both sides
x = 108/9
x = 12
Hence, the value of x is x = 12
