Unless I am misreading, the question, or don't know all of it, there can be an infinite number of similar shapes. Three are give to you at the bottom of this answer, but there are many more possibilities.
I think the answer is 22mn2+66m2n-64 since there are no more like terms
The result can be shown in both exact and decimal forms.
Exact Form:
2
3
Decimal Form:
0.
¯
6
Greater because a centimeter is smaller than an inch.