x + 60 = 100 (because they are vertical angles, which means that because they are directly opposite of each other, they are of the same measurements).
Solve for x. Isolate the x, subtract 60 from both sides
x + 60 = 100
x + 60 (-60) = 100 (-60)
x = 100 (-60)
x = 40
40° should be your answer
hope this helps
