Final answer:
David used 4 4/9 gallons of water in total for the plants, by multiplying the water per plant (8/9 gallons) by the total number of plants (5).
Step-by-step explanation:
David watered 5 plants, and each plant got 8/9 gallons of water. To find the total amount of water used, multiply the amount each plant got by the number of plants: 5 plants × 8/9 gallons per plant = 40/9 gallons. Since 40/9 is an improper fraction, it can also be expressed as 4 4/9 gallons in mixed number form, which is the simplest form.