A different approach to solving the problem than the one shown in the link provided by the other tutor....
The salt is 3% of the 240 gallons, or 7.2 gallons.
When water is evaporated, the amount of salt remains at 7.2 gallons.
If the solution is to be 5% salt, those 7.2 gallons need to be 5% of the solution, so the new total amount of the solution needs to be 7.2/0.05 = 144.
Since the original solution was 240 gallons and the new solution is 144 gallons, the number of gallons of water that needed to be evaporated is 240-144 = 96.
