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°