Another maths question

Don't put any new purchases on it (might be what PeterS means) without reading all the conditions as all sorts of stuff can apply like having to pay off the entire interest free amount before anything is paid off new expenditure which will start attracting fresh interest. Use it as an opportunity to make a start in completely ridding yourself of the debt. When the interest free period expires, check out transferring your reduced balance to another interest free cc.

Even when you can pay off the entire cc bill at the end of each month you're still not technically solvent unless you've got the cash to pay the next month's bills, and are instead choosing to pay by cc to get either cashback on cc expenditure or get interest on that cash you could be using to pay bills. There is another advantage which is to build up a credit rating by being responsible with a credit card rather than always paying with cash.

Don't use any of them - cut them all up! (after getting that 0% transfer). If you're up to the limit with one, don't start racking it up on another.