isosceles triangles means that the two bottom angles and sides are equal
therefore, you can set R and T equal to each other:
(15x-31)=(9x+11)
(get x to one side)
15x=9x+42
6x=42
x=7
now you can plug x back into the equations:
15(7)-31
105-31
74
R and T = 74
all triangles' internal angles = 180
therefore you can add the two angles then subtract them from 180
74+74=148
180-148=32
S should be 32 :)
