The first thing to notice with this question is that the volume of the tank is given in cm3 yet the rate at which the water leaks is in litres, so a conversion of units will be neccessary. We know that there are 1000cm3 for every litre so 45000cm3 is equivilent to 45 litres (45,000/1000 = 45). So what do we know now? Well the tank of water contains 45 litres, and every minute 0.75 litres is lost, so our objective is to find out how many miuntes go by before the tank is empty. In other words how many 0.75s go into 45, luckily division can help us out. 45/0.75 = 60 minutes.
