Answer:
70.45 gallons per capita per day
Explanation:
Per capita means for each person. so for instance if each person int he city generated one gallon per day it would be 39,458 per day.
In other words we want to know how much each person would have to produce per day to make 2.78 million per day. So the idea is 39458 has to be multiplied by something to get 2.78 milion. There you just use algebra.
39458x = 2,780,000
x = 2780000/39458
x = 70.45
So each person on average uses 70.45 gallons per day. You can check too by multiplying this by 39458 representing each person.