Answer:
x = 8
Step-by-step explanation:
The sum of two interior angles in a triangle is equal to the exterior angle that's supplementary to the third interior angle:
7x + 6 + 22 = 9x + 12 add like terms
7x + 28 = 9x + 12 export like terms to the same side of the equation
28 - 12 = 9x - 7x
16 = 2x divide both sides by 2
8 = x
