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3 x 90 = 270
-3 x 90 = -270 -3x = 90 x = -30
The answer is 3+0.9+0.01
The sum of the interior angles of a quadrilateral is 360 degrees so if 3 of them are right angles (90 °) the remaining fourth angle must also be 90 °. 360° - 3x90° = 90°