A car radiator needs a 40% antifreeze solution. The radiator now holds 12 liters of a 20% solution..

A car radiator needs a 40% antifreeze solution. The radiator now holds 12 liters of a 20% solution. How many liters of this should be drained and replaced with 100% antifreeze to get the desired strength?

A car radiator needs a 40% antifreeze solution. The radiator now holds 12 liters of a 20% solution.