fuel taxable benefit

In the BPP revision kit there is a question which stated an employee was given a new car and the firm paid for all petrol costing £1500 without reimbursement. In the answer the fuel calculations was 22600 X 25% (this was the car benefit percentage) This came to £5650. I don't understand why the £1500 figure wasn't used. £1500 was completed omitted in the answer to this question. I'm sure i'm missing something in my understand but after going back through the lectures i still cant work this out.