12:00 P.M. to 7:00 P.M. is a total of 7 hours.
4:00 P.M. to 7:00 P.M. is a total of 3 hours.
This means that from 4:00 p.m to 7:00 P.M. this represents 3/7 of what was lost from 12:00 P.M. to 7:00 P.M.
After knowing this, after doing 11,600 - 6,800 = 4,800
4,800 represents 3/7 of what was lost for 7 hours.
We then divide 4,800 by 3 which gets 1,600.
Because we know that 1,600 represents 1/7 of how much water was lost, we just have to multiply by 7, which gets 11,200. After adding 11,200 to how much water was left at 7:00 P.M. which was 6,800. 11,200 + 6,800 = 18,000
This means that the pool originally had 18,000 gallons in the pool.
You can also check your work by doing 18,000 - 4(1600), which becomes 1800 - 6400 which gets you 11,600.
Your answer is -2/1 but reduced it's -2.
