Calculating Water Usage for Plant Care

Alice bought a new plant for her garden. The plant requires a specific amount of water to thrive. Each day, Alice waters the plant with 3/4 of a gallon of water. After five days, she realizes that she has watered the plant a total of 2/3 of a gallon of water over those five days. What is the total amount of water, in gallons, that Alice should have used for the plant over the five days?