Question 150859
The sum of the angles in a triangle is 180.
The sum of angle T plus the exterior angle at T is also 180 (since the two angles (T and exterior at T) form a straight line).

Thus, the exterior angle at T equals the sum of the other two interior angles

Let S be the angle at S, then R = 2S
The ext
S+2S = exterior angle T
3S = 75
S = 25
R = 2*25 = 50
T = 180-75 = 105