Hey there! :D
Use proportions to figure out the similarity and the missing side.
The smaller polygon has a side of 4.
[tex] \frac{4}{20} = \frac{x}{28} [/tex]
[tex]20*x= 4*28 [/tex]
[tex]20x=112[/tex]
[tex]x= 5.6 [/tex]
The corresponding side of the larger polygon is 5.6.
I hope this helps!
~kaikers