2 Answers

To be a parallelogram, both pairs of opposite sides must be equal in length, i.e. LM=ON and LO=MN
LM=ON
7x4=8x8 (7x)
4=x8 (+8)
4=x
x=4
LO=MN
5y7=x9 (sub x=4)
5y7=49
5y7=5 (+7)
5y=2 (/5)
y=2/5
Therefore,
x=4
y=2/5

opposite sides are congruent...did you make a diagram ? do it now !
You have BAD information in your problem !
ON = LM
8x  8 = 7x  4
solving for x gives: x = 4
However, if x = 4, then NM (which you say is (x  9)) would be NEGATIVE...
CAN NOT HAVE A NEGATIVE DIMENSION !
Check your problem, check your post...repost the problem correctly !