Question 727710
https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcQ7406FcocKuV2BVB0uES8BpiHy_EVmnoXmw26eRsOsUAEFJbKccw site for parallelogram ABCD

in which side ab // cd & ab=cd (opp.sides of paralleogram),bc //ad &bc=ad (opp.sides of paralleogram)

Ab=cd   2x-7=x+y  ---(1) 2x-x-y=7 or x-y=7  (3)
bc=ad   x+3y=2x-y-1  (2) x-2x+3y+y=-1 or -x+4y=-1 or x-4y=1  (4)
 solve these(3) &(4) two linear equations

  x-y  =7    (3)
  x-4y =1   (4) Subtract(4)-(3)
  - +   -
-------------
    3y = 6 Or y=2 Substitute y=2 in (3) we get x-2=7 or x=9
Thus x=9 y=2 
[ab 2*9-7=9+2 or 18-7 = 11  which are opp sides // &equal similarly bc &ad]