Samantha has a rectangular shaped fish tank in her room. the tank has a height of 2.5 ft, a width of 2.1 ft, and a length of 3.9 ft. approximately how much water can her fish tank hold?

When you are trying to find how much something fits in a specific place you are looking for volume. Volume=length x width x height. Therefore you would substitute your given into the formula. 

3.9 x 2.1 x 2.5 and get 20.475.

Hope this is useful :)