Sum of the angles of the trapezoid (quadrilateral) add up to 360°, so based on available information mâ A + mâ B + mâ C + mâ D = 360° relates to mâ A + 25° + 155° + 117°.=360° So, mâ A = 360° - (25°+155°+117°) mâ A = 360° - 297° mâ A = 63°
