The answer would be 108 degrees because in an isosceles triangle, the two base angles are equal to each other.
So you would start off by setting 2x - 20 equal to x + 8.
2x - 20 = x + 8
then solve for x
x = 28
Substitute x into either equation
28 + 8
solve
28 + 8 = 36
Both base angles are equal to 36. So take 180 and subtract 36 twice.
180 - 36 - 36
solve
180 - 36 - 36 = 108 degrees