The angles of a quadrilateral are x, 5x+15°, 3x-25°, and 4x-20°. Find the measure of the largest angle of the quadrilateral.

The sum of the measures of the interior angles of a quadrilateral = 360°........so we have

x +  [5x + 15] + [3x - 25] + [ 4x - 20]   = 360      simplify

13x - 30   = 360     add 30 to both sides

13x  = 390      divide both sides by 13

x = 30

The largest angle  is  5x + 15  =   165°