The formula for circumference is  \pi times the Diameter or 2 \pi r r being the radius. C=2.5 is most likely the circumference and you need to solve for either the diameter or radius
Then pi times 75 is all you have to do
reallly cause I thought it was Pi times diameter times radius two times
nope I am sorry if my answer made it confusing
no no u acc helped a lot thanks so much
Glad you understand