Three angles of a quadrilateral are 75°, 90° and 60°, the fourth angle is
Let the fourth angle of the quadrilateral be x°.
By angle sum property, the sum of interior angles of a quadrilateral is 360°.
⇒∠A+∠B+∠C+∠D=360°
⇒75°+90°+60°+x°=360°
⇒x°=360°−(75°+90°+60°)
⇒x°=360°−225°
⇒x°=135°
Hence, the fourth angle of the quadrilateral is 135°.