Two angles are supplementary if they add up to 180 degrees. We have then: m ∠ DAB + m ∠ ABC = 180 Substituting: (85 - 2x) + (90 + x) = 180 From here, we clear the value of x: -x + 175 = 180 x = 175 - 180 x = - 5 Let's try now that it is a parallelogram. The opposite angles of a parallelogram are equal in measure: m ∠ DAB = m ∠ BCD 85 - 2x = 80 - 3x 85 - 2 (-5) = 80 - 3 (-5) 85 + 10 = 80 +15 95 = 95 Answer: x = -5 m ∠ DAB = m ∠ BCD (It is shown to be a parallelogram)