The angle 130 degrees is 1 part of a straight line, and straight lines are 180 degrees. The angle right next to it, which is part of the triangle, is 50 degrees, because 130+?=180, so ?=50 degrees.
The degrees of a triangle always add to 180 degrees. Because we now know 2 of the angles, we can easily solve for the third:
50+53+x=180
x=180-50-53
x=77 degrees
