How much water should I put in the gas tank of my car?
user
I don’t know how to calculate that but I can tell you how to find out.
assistant
Thanks.  I have a small pickup truck.
user
The gas tank has a capacity of 18 gallons. 
Let’s look up how much gasoline is in that volume:
assistant
How much water should I put in the gas tank of my car?
user
I don’t know how to calculate that but I can tell you how to find out.
assistant
Thanks.  I have a small pickup truck.
user
Got it, let’s see... that looks like a 2002 Chevy S-10.
assistant
How much water should I put in the gas tank of my car?