The owner of a pet shop in Reading bought a certain number of hamsters and half that many pairs of parakeets. He paid £2 for the hamsters and £1 for each parakeet. For every pet he charged an amount that was 10% higher than its cost price.

After all but 7 of the little critters had been sold, the owner found that he had taken in an amount of money equal to what he had originally paid for all of them. Supposing he goes on to sell the remaining animals, still at a 10% mark-up, what is his profit?