Supply of milk in the morning = 32 litres
Supply of milk in the evening = 68 litres
Total supply of milk per day = (32 + 68) litres = 100 litres
Now, cost of 1 litre of milk = ₹15
Cost of 100 litres of milk = 15×100 = ₹ 1500
Therefore, ₹ 1500 is due to the vendor per day.