The upper right corner is perpendicular to the bottom.

x = sqrt(80^2 - 55^2) = 58

& ltC = arctangent (55/(80-58)) = 68 degrees.

The other internal angle of the quadrilateral = 1 12 degrees.

a^2+b^2-2 ABC OS 1 12 = 80^2

A^2 = x^2 + (55-B)^2

B = 32

A = 62