"William Claspy" wrote in message
My guess was 6(pi) inches. It's C=pi(d), so if we add six inches to d
(which we had converted from feet to inches), we have C=pi(d+6). Balances
out with 6(pi). No?

No. You're thinking correctly, but you only got halfway there. You're
actually increasing the diameter by a whole foot (6 inches each side).

Joe F.