Answer:
1/2 gallons
Step-by-step explanation:
since 1/3of the tank is already full and another 4 gallons fills it up
4 gallons= 2/3 of the tank or the tank is 6 gallons total
75% is equal to 3/4
6*3/4=4 1/2 gallons
since it is 1/3 or 4 gallons full
4 1/2 -4= 1/2