Triangle RTS is isosceles. You can tell because both of the base angles have the same measure. That means that RT must also be 15. Triangle UTR is equilateral because all 3 angles have the same measure. UT is x - 5 and is equal to RT which is 15, so x - 5 = 15, and x is 20.
Since triangle UTR is equilateral, angle URT is 60 degrees. Angle SRT is linear with angle URT, so angle SRT is 120 degrees. That means the other 2 angles must add to 60 degrees, making each one worth 30 degrees. Angle RTS says 3y, so 3y =30, and y = 10
