Answer:
31 units
Step-by-step explanation:
When the figure is a parallelogram, opposite sides have the same measure:
AD = BC
3x +7 = 5x -9 . . . . . . substitute given expressions
16 = 2x . . . . . . . . . . . add 9-3x
8 = x . . . . . . . . . . . . . divide by 2
Use this value of x in the expression for AD to find its required length:
AD = 3(8) +7 = 24 +7
AD = 31 . . . . units
The length of segment AD must be 31 units for ABCD to be a parallelogram.