Answer:
x = 10
Step-by-step explanation:
The exterior angle is equal to the sum of the opposite interior angles
12 +10x = 81 + 31
Combine like terms
12 +10x = 112
Subtract 12 from each side
12-12+10x = 112-12
10x= 100
Divide each side by 10
10x/10 = 100/10
x = 10
