We are given an isosceles triangle.
An isosceles triangle has corresponding angles of corresponding sides same.
Therefore, other angle is also of (3x+7) degrees.
(5x+13) and (3x+7) makes a linear pair.
Therefore,
(5x+13) + (3x+7) = 180
5x +13 + 3x +7 = 180.
8x +20 = 180.
Subtracting 20 from both sides, we get
8x +20-20 = 180-20.
8x = 160
Dividing both sides by 8, we get
x = 20.
Therefore, correct option is 3rd option.
