4/5 if you are reducing it. If you are dividing it, it is 1.25
take 360 and divide by the number of sides
regular means the sides are equal therefore the angles are equal
360 /4 =90
360 /5 =72
B
The diameter would be 24 and the radius would be 12 I believe :)
Plug in to each in the function.
Hope this helps.
頑張って!