The answer would be 10! I divided the number of plants that you can water with 4 gallons (14) by, well, the number of gallons it takes to water them (4) and got 3.5 (14 / 4 = 3.5), the number of plants you can water with one gallon. I then divided the number of plants you need to water (35) by the number of gallons it takes to water one plant (3.5) and came up with 10. I hope this helps you!