If ''how much water is in each lake?'' refers only to Lake Superior, Michigan and Huron, this should be the answer.
The question gives us some information on the lakes' sizes which we can use to find the answer.
S-1720=M
S-(1720+330)=S-2050=H
Now we do some basic algebra and find the value of S.
S+(S-1720)+(S-2050)=4930
3S-3770=4930
3S=8700
S=2900
Now we use S' value to find the value of M and H.
2900-1720=1180=M
2900-2050=850=H
Answer: Lake Superior contains 2900 cubic miles of water, Lake Michigan contains 1180 cubic miles of water, and Lake Huron contains 850 cubic miles of water.