math
posted by jenna .
what is the exact circumference of a circle with a diameter of 13 inches?

what is the formula PI*diameter=Cicumference used for?

i am confused??

the pi is 3.14

C=PI*diameter.
You need to get this down. 
okay but the options i have to choose from are:
a. 26Pi in.
b. 6.5Pi in.
c. 13Pi in.
d. 42.25Pi in.
e. 169Pi in.
i think it's a. right?