A man purchases milk for three consecutive years. In the first year, he purchases milk at the rate of 7.50 per litre, in the second year, at the rate of 8.00 per litre and in the third year, at 8.50 per litre. If he purchases milk worth 4,080 each year, the aver-age price of milk per litre for the three years is

• A. 7.68
• B. 7.98
• C. 7.54
• D. 7.83