Idon't understand how to do it

Hi there! The answer is 75.

Spring Middle School:
60 gallons of water circulate every 1/5 hour, so multiplying by 5 gives the following: 300 gallons of water circulate every hour.

Bay Middle School:
75 gallons of water circulate every 1/3 hour, so multiplying by 3 gives the following: 225 gallons of water circulate every hour.

Therefore, 75 litres circulate more per hour at Spring Middle school compared to Bay's.

4should be the last one n=4