Manny's cleaning supply store receives a mixture of 80% detergent and 20% water in 15-gallon buckets. Manny would like a mixture of 60 detergent and 40% water in a 5 gallon buckets. To make this he combined some 80/20 mixture with some pure water in each 5 gallon bucket. How much gallons of pure water does Manny add to each 5 gallon bucket. Express your answer as a decimal to the nearest hundredth.