Well, the only way you could find the length and width given these values is if the length and width are equal. Otherwise you have two unknowns in the equation as opposed to one. If Length = Width, You could take:

Volume = Length*Width*Height and rewrite it as:

Volume = Length*Length*Height

And then substitute the appropriate values and solve it. Does the problem specify that the base of the object is a square or something along those lines?