Ok it might be easy but i don't get it

It would be D, 11.25. There are 1440 minutes in a day, making it 1440 fl oz per day. You just convert that to gallons by dividing it by 128 (128 fl oz=1 gal).

First find how many ounces of water are dripping per day:

1 ounce per minute
(60 minutes in an hour)
1 x 60  = 60 ounces per hour
(24 hours in a day)
60 x 24 = 1440 ounces per day

Now we convert ounces to gallons. (there are 128 ounces in a gallon)

# of ounces/ # of ounces in a gallon = # of gallons
1440 ounces / 128 ounces per gallon = 11.25 gallons

This means the faucet is dripping 11.25 gallons per day.

Side note: That's a some money flowing down the drain!