This problem needs to use the mean inequality in high school. Under the third radical sign, (abc) is less than or equal to (a+b+c)/3, and when a=b=c, an equal sign is taken.

The volume is x (30-2x) (30-2x) =1/4 * 4x (30-2x) (30-2x).

Because [4x (30-2x) (30-2x)] is less than or equal to (4x+30-2x+30-2x)/3=20.

So when 4x=30-2x, x=5 and the volume is the largest,1/4 * 4x (30-2x) (30-2x) =1/4 * 203 = 2000.