The figure gives rise to two equations.
6y = 90
5y +3x = 180
There are several ways to go about this. Here's one.
2y = 30 . . . . . . divide the first equation by 3
(5y +3x) -(2y) = (180) -(30) . . . . subtract the equation above from the 2nd
x + y = 150/3 = 50 . . . . . . . . . . divide by 3
The appropriate choice is the 3rd one, ...
50