A large number of buses stop at the bus stop at the end of old hall lane.The 42 bus stop there every 6 minutes,the 43 bus stops there every 8 minutes and the 45 bus stops at every 15 minutes.If all the buses stop at the old hall lane stop at 4.00pm, write down the total number of buses that will call at the stop between 4.20 and 4.50 pm.