Three angles of a quadrilateral measure 56°, 115° and 84°. Find the measure of the fourth angle.
Let the measure of the fourth angle be xo.
Since the sum of the angles of a quadrilateral is 360°, we have:
∴ 56° + 115° + 84° + x° = 360°
∴ 255° + x° = 360°
∴ x° = 105°
Hence, the measure of the fourth angle is 105°.