those two angles have to add up to 180° as that is a straight angle, so 5x - 10 + 6x + 10 = 180. combine like terms to get 11x - 10 + 10 = 180. the 10 cancels, so 11x = 180. divide both sides by 11 to get x = approximately 16.36.
FYI - I CANNOT TELL IF THAT ACTUALLY SAYS 5