You are a manager of a water supply company in Sydney. You have two plans for your customers as follows: Plan 1: Bill = 25 + 0.06 L; and Plan 2: Bill = 40 + 0.04 L; Where, 'Bill' is the monthly bill in dollars and 'L' is the monthly total use of water in litres. (a) Find the break-even level of total use of monthly water in litres. (3 marks) (b) If your customer's average monthly use of water is 500 litres, advise which plan would be suitable for your customer? (4 marks) (c) If your customer's average monthly use of water is 900 litres, advise which plan would be suitable for this customer? (4 marks) (d) If there is a $10 reduction in the monthly fixed fee in Plan 2, then what would be your advice to the customer whose average monthly water use is 500 litres? (4 marks)