Question

What sides measurements do i need to know to answer this problem?

Answer 1

You can pick any sides that have numbers on both figures. LM and CD are useful, because CD = 1. That means any side in the larger figure will be 1.6 times the corresponding side in the smaller figure.
.. LM/CD = MN/DE
.. 1.6/1 = x/2
.. 2*1.6 = x = 3.2