Ignore lines VS and SU. They're unnecessary clutter.
Triangle VRT is a right triangle with angles T = x, R = 60, V = 90
For any triangle, the angles must add to 180
T+R+V = 180
x+60+90 = 180
x+150 = 180
x = 180-150
x = 30
Or you could note that R+T = 90 Solves to T = 30 since triangle VRT is a right triangle. The rule with any right triangle is that the acute angles are always complementary (aka they add to 90 degrees).
