Hello hello!
Solving this is simple, just remember the vertical angles theorem. Due to this theorem, you are able to conclude that x+40 and 60 are equal in terms of their angle measure. This means that to solve this, we need to set both sides equal to each other and solve for x, and plug it in!
STEP ONE: 60 = x + 40
DO: Subtract 40 from both sides.
STEP TWO: 20 = x
DO: You've answered the question!
ANSWER: x = 20