Answer: improper fraction: 69/28
Mixed number: 2 13/28
EXPLANATION
Just add the fractions. Find common denominators. We can multiply 5/7 by 4 and 3/4 by 7 to get common denominators
So
5/7 x 4 is 20/28
3/4 x 7 is 21/28
And 1 gallon is just 1/1 so we could also multiply by 28
1/1 x 28 = 28/28 (which also equals 1)
Now we can add
20/28 + 21/28 + 28/28 = 69/28
You can simplify to 2 13/28