The outside angle is equal to the sum of the two opposite inside angles.
So you have:
X + 82 = 2X+10
Subtract 1 X from each side:
82 = X+10
Subtract 10 from each side:
x = 72
Now you can calculate the exterior angle by replacing x with 72:
2x+10 = 2(72) +10 = 144+10 = 154