A record has a central label and the rest is exposed vinyl.
So first you need to subtract the central label diameter from the total diameter of the record to figure out how much is exposed vinyl on both sides of the label--> 12 - 4 = 8
Half of this exposed vinyl is on either side of the label, so the width of the exposed vinyl is 4 inches.
This makes sense: 4 inches of vinyl, then 4 inches of label, then 4 inches of vinyl = 12 inches in all.
There is no need for pi.
If the question would ask for the area of the exposed vinyl, then pi would be needed.