Let's begin by listing out the information given to us:
Angle U = 27°
TU is tangent to S implies this is a right triangle
Angle T = 90°
The sum of interior angles in a triangle is 180 degrees
U + T + S = 180°
⇒27 + 90 + S = 180
⇒S = 180 - (90 + 27) = 53
S = 53°
