Yesterday my mother asked me to buy some stamps. Stamps, in the land of BrainBashers, are available in 2p, 7p, 10p, 15p and 20p denominations. For three types of stamp I was asked to buy five of each. For the other two types of stamp, I was asked to buy six of each. Unfortunately I forgot which I was supposed to buy five of and which to buy six of. Luckily my mother had given me the exact money required to buy the stamps, £3.00 and the shopkeeper was able to give me the correct stamps. Which stamps did I buy?