Cost of milk in each year = Rs 4,080
Cost of milk in the first year = Rs 7.50 per litre
Cost of the milk in the first year = 4,080 ÷ 7.50 = 544 litre
Cost of milk in the second year = Rs 8.00 per litre
Quantity of milk in second year = 4,080 ÷ 8 = 510 litre
Cost of milk in the third year = Rs 8.50 per litre
Quantity of milk = 4,080 ÷ 8.50 = 480
Quantity of milk purchased in three years = 544 + 510 + 480 = 1,534 litre
Total purchase of milk in three years = 4,080 × 3 = Rs 12,240
Average price of milk per litre for three years
==Rs.7.98