Given parallelogram abcd, find the lengths and angles required

Co-interior properties. 180 degrees = two co-interior angles.

180 = (2y+50) + (3y+40)
180 = 5y + 90
90 = 5y
/5     /5
18 = y

Angle 1: 2y + 50
              2(18) + 50
              36 + 50
              86

Angle 2: 3y + 40
              3(18) + 40
              54 + 40
              94

86 + 94 = 180 so it is true.

Now the sides.
On a parallelogram, 5x+2 and 8x-7 must be equal

5x + 2 = 8x - 7
        2 = 3x - 7
        9 = 3x
       /3    /3
        3 = x

Side 1: 5x + 2
            5(3) + 2
           15 + 2
           17

Side 2: 8x - 7
            8(3) - 7
            24 - 7
            17

Both sides are equal; 17.

Angle 1: 86
Angle 2: 94
Sides: 17