A factory owner purchases two types of machines, `A` and `B` for his factory. The requirements and the limitations for the machines are as follows: Machine Area occupied Labour force Daily output (in units) `A` `1000\ m^2` `12\ m e n` `60` `B` `1200\ m^2` `8\ m e n` `40` He has maximum area of `9000\ m^2` available, and 72 skilled labourers who can operate both the machines. How many machines of each type should he buy to maximise the daily output?