In an isosceles triangle two angles are equal. The measure of angle A is 20 degrees more than three times angle B. Angle B has the same measure as angle C.
The sum of the three angles is 180 degrees. If the measure of angle C is X.
X + X + 3*X + 20 = 180
=> 5X = 160
=> X = 32
The measure of angle C is 32 degrees.