To get the angle x + 51, We need to draft out the triangle having the unknown and the two angles that are vertically opposite to 80 degrees and 60 degrees.
Total internal angles in a triangle is 180 degrees.
Therefore, x +51 = 180 - (80 +60)
x + 51 = 180 - 140
x + 51 = 40 degrees
Subtracting 51 from both sides give
x = -11
