The expression to calculate the total gallons of water used in a 5-minute shower is:
total gallons = 7.5 gallons/minute × 5 minutes
Multiplying the rate of water usage (7.5 gallons/minute) by the duration of the shower (5 minutes) gives:
total gallons = 37.5 gallons
Therefore, a 5-minute shower would take about 37.5 gallons of water.