need help please

7. How would you set up a series of 6 tubes with a 1:2 serial dilution, such that you end up with 4ml of solution in each tube? What is the final dilution in each tube? 8. Six tubes are placed in a rack. To all six tubes, you add 3ml of water. Then 2ml of serum is added to the first tube and mixed well. You then transfer 1ml of that to the second tube and again mix well. You continue the transfer of 1ml of mixture from one tube to each subsequent tube, finally discarding 1ml from tube 6. What is the dilution of serum contained in tube 6