TRICKY MATHS PROBLEM!!! HELP!!! Involves algebra I can't do!!!!?

[Liz-face]

Each summer weekend Tom drives his new ice-cream truck van to the local coastal towns. It has an accurate digital fuel gauge that tells him exactly how much fuel he uses on a trip. He notices that his van’s rate of fuel consumption is the same every weekend. He leaves home with his fuel tank nearly empty so he has to fill up at the local petrol station first. He sells only enough ice-creams so that his takings are $100 plus the price of fuel since filling up, based on the price paid at the petrol station.

On the first weekend Tom brought petrol at $1.46 per litre so he decided to charge 85c per ice-cream. He travelled 328km and sold 152 ice-creams to make his required total.

On the second weekend Tom bought petrol at $1.40 per litre so he decided to charge 80c per ice-cream.

On the third weekend petrol was $1.45 per litre so Tom increased the price, sold 13 less ice-creams, and used 3 litres less fuel than the second weekend.

HOW MANY LITRES OF FUEL DOES TOM USE IN WEEK 2?

[medke]

How did you come up with the answer of 2? Are you guessing and hoping someone will give you the answer or did you really do the work and have a hypothesis worked out to justify your work?