What is the value of x?

How I got this

Use the exterior angle theorem. This theorem says adding any two remote interior angles of a triangle is the sum equal to the exterior angle.

The interior angles x and 70 add to x+70, which is equal to the exterior angle 100

x+70 = 100

x+70-70 = 100-70

x = 30

Another route is to mark y as the angle adjacent to 100, and this angle y is inside the triangle. It is the third missing angle. Solve 100+y = 180 for y to get y = 80

The triangle has interior angles 80, 70 and x. They add to 180 leading to

80+70+x = 180

x+150 = 180

x+150-150 = 180-150

x = 30

answer: it's d

step-by-step explanation: