Data Sufficiency

Am i missing something ???

I DONNO HOW TO TACKLE OPTION B.

PLS HELP.

In Isosceles triangles 2 angles are same.

we need to find the angle R

from 1 angle T is 100 means the measure of the other two angles should be 80 and so angle R is 40 (isosceles triangle ) sufficient.

from 2 angle s is 40 means there are two possibilities
1. s=40 and other 2 angles t=70 r=70
2. s=40 or (t or r =40) and remaining angle is 100
so insufficient.

so the answer is A