I am still learning, and am most likely incorrect.
I believe you remove the 3's since their not needed, and do this:
2x = 4x + 6 - (2x)
so then just ignore "x" and do this:
2 = 4 + 6 - 2
2 = 10 - 2
2 = 8
x = 8
28/11.2 = 2.5
since they are similar and openly stated as parrallelograms, you know that they have a scale of the longest edge of EFGH to the longest edge of JKLM