Answer:
20 ounces
Explanation:
For this type of problem it is best to work backwards.
If David has 18, and Charlie gave him 1/2, then Charlie has 36 because 18x2=36. Barbara has 60, because 36/3= 12 and 5x12=60. Then, Amanda has 80 because 60/3=20 and 20x4= 80. But, we need to subtract 60 because the problem asks how many ounces of water does Amanda still have. So, 80- 60(The amount of water she gave to Barbara)=20.