Plz help!!! I will brainliest and no links!! Also plz explain ur answer!!

Mrs. O and her family decided to go to Disneyland for vacation. When they left their house, they had to put 3/4 of a tank of gas in their car. When they got to St. George, they put 1/2 of a tank of gas in their car. How much more gas did they put in the car the first time?