Use the Isosceles Triangle Theorems. The Base Angles Theorem. If two sides of a triangle are congruent, then the angles opposite those sides are congruent. Converse of the Base Angles Theorem. So, X + 8 = 2X - 20
             subtract x from both sides  -X     -X
              new equation              8 = X - 20
           add 20 to both sides           +20   +20
                                     28 = X
Angle B = Â Â X + 8 Â Â Â Â
sub 28 for X Â (28 + 8 =Â 36)