The water cooler started with 6 1/2.
To solve this question easily, we'll use a common denominator, which is 12.
6 1/2 = 6 6/12
It leaked 2 5/6 which is 2 10/12
6 6/12 - 2 10/12 = 3 8/12
She adds 1 1/4 gallons = 1 4/12
3 8/12 + 1 4/12 = 5
I hope this helps! Good luck! :)