A drum contains 120 litres of a mixture of two paints, Red and White. 30 litres from this mixture is taken out twice and replaced with the same amount of White paint both times. If the final quantity of Red paint in the mixture becomes 36 litres, what was the initial quantity of White paint?

A vessel has 20 litres of milk. From this vessel, 5 litres of milk is taken out and replaced by water. The process is repeated once more. Find the quantity of milk (in litres) remaining in the vessel.

A shopkeeper mixes 40 kg of rice costing ₹30/kg with 60 kg of rice costing ₹50/kg. What is the average price (in ₹/kg) of the mixture?