if a line is drawn across the shape connecting two of the angles it makes two triangles. The sum of the angles in a triangle is 180 degrees.
Since this shape makes two triangles the sum of the inside angles is 2 * 180 = 360 degrees
(2x - 17) + 90 + x + 59 = 360
combine like terms
3x + 132 = 360
3x = 360 - 132
3x = 228
x = 76