Question 1: this is simple adding
do the fractions first 1/4 + 3/4 = 4/4 or 1
then the whole numbers 1+1+1=3 gallons
Question 2: do it the same as the first you can make 1 1/2 into a mixed number which is 3/2 and make 4 into 8/2 then subtract 8/2 - 5/2= 3/2 or 1 1/2
Question 3: make into mixed numbers 5/3+5/3= 10/3 or 3 1/3