the sum of all interior angles in a polygon is
180( n - 2 ), n = number of sides in the polygon.
this one is a QUADrilateral, so it has 4 sides, thus its interior angles add up to 180( 4 - 2), or 360°.
thus 75 + 104 + 59 + ∡N = 360, ∡N = 360 - 75 - 104 - 59.
