20 points!
question is in image, and answer choices are here:
5, 4, 8, 10

x is equal to 4

Step-by-step explanation:

A triangle's angles sums up to 180°. So we already know that the three angles in this triangle add up to 180°. The equation would be as following.

(18x - 12) + 15x + (10x + 20) = 180

We first add like terms together.

43x + 8 = 180

We then substract 8 on both sides.

43x = 172

We finally divide 43 on both sides.

x = 4