The answer would be 129 degrees!
x + 51 = 180
x + 51 - 51 = 180 - 51
x = 129
the angle below 51 degrees would be complementary angles with x and so it would also have 51 degrees above x. 51 degrees and x are supplementary angles. supplementary angles are two angles that have a sum of 180.
hope that helps!!
