Answer this question, thx for the help

How many sides does a regular polygon have if each exterior angle measures 72a.3b.4c.5d.6

On a piece of paper graph f(x)=5•(0.4)^x

Abicycle training wheel has a radius of 3 inches. the bicycle wheel has a radius of 10 inches. approximately how much smaller, in square inches and rounded to the nearest hundredth, is the area of the training wheel than the area of the regular wheel? *