Katie and Will have some balloons, some are red and some are blue.

First, Katie blew up a red one. After her first puff her balloon had a circumference of 24 cm. Her second puff added 1/2 as much again to that. Her third puff increased it by 1/3. Her fourth puff increased it by 1/4 and her fifth puff by 1/5, her sixth puff increased it by 1/6 and at the beginning of her seventh puff it went

Next, Will blew up a blue balloon. After his first puff his balloon had a circumference of 14 cm. And, just like Katie's, his second puff added 1/2 as much again to that and his third puff increased it by 1/3, his fourth puff increased it by 1/4 and so on. His balloon burst at exactly the same size as Katie's at the beginning of a puff.

How many puffs had Will done before his balloon burst?