120
All triangles have total interior angle of 180 degrees. You can find the missing angle of triangle STU to be 60 degrees. A straight angle is 180 degrees. Angle SUY is a straight angle, therefore totaling to 180 degrees. We already have one part of the angles, 60. So logically, 180 - 60 would bring us the missing angle. 180 - 60 = 120.
