For context, all triangles' angles will always add up to 180°. The outside angle of S is supplementary to the inside angle, so in order to find S:
<u>180 - 153 = 27°</u>
<TSU = 27°
S = 27°
U = 88°
As mentioned before, angles of triangles will add up to 180. In order to find the missing angle (?) we will add the other two sides and subtractthemfrom180.