The areas of two similar rectangles are 80 square feet and 500 square feet.

what scale factor applied to the smaller rectangle will give the larger rectangle?

25/64
25/4
5/2
5/8

So, we have the area, easy. Multiply each of the answers by 80.
(Hint: You can change the fractions into decimals and do it then. It'll be much easier than trying to multiply it by the fractions.)
25/64=.390625 (I would round this to .39)
25/4=6.25
5/2=2.5
5/8=.625

Which one, when multiplied by 80, gives you 500?
80*.390625=31.25
80*2.5=200
80*.625=50.

Leaving 6.25*80=500. Meaning, 25/4 is your answer.