If 'P' means 'divided by', 'T' means 'add', 'M' means 'subtract' and 'D' means 'multiplied by', then what will be the value of the following expression?
A flask has two holes. The 1st hole alone makes the flask empty in 9 minutes and 2nd hole alone makes the flask empty in 16 minutes. If water leaks out at a constant rate, how long in minutes does it take if both the holes together empty the flask?