Answer:
78
Step-by-step explanation:
Hello
A Parallelogram is a flat shape with opposite sides parallel and equal in length, in this case .
side AB = side DC
9x+3 = 11x-17
let x
[tex]9x-11x=-17-3\\-2x=-20\\x=\frac{-20}{-2} \\x=10[/tex]
let's replace the value of x in the equation of the side BC
[tex]BC=6x+18\\BC=6*(10)+18\\BC=78[/tex]
Have a nice day
