We could use Euler's polyhedron formula:

Answer:
x=5.75
Step-by-step explanation:
As you can see, EH and FG are congruent, which means that the measurements must be the same.
You have 4x+5=28
That's already an equation! Now you solve it:
4x+5=28
4x=28-5
4x=23
x=5.75
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