check my work w/ this word problem

ok so i'm not sure if my answers are right

An open box is to be formed by cutting four identical squares from the coners of a sheet of metal 20cm by 20cm, and folding up the metal to form sides. the capasity of the box must be . what is the side length of the squares?

**this is what i got **

**let x be the length of the missing sides**

**x(20-2x)(20-2x)=588**

** **

** **

**where is got a factor of (x-3)**

**and was left with **

**wich gave me x=15.44 or x=1.55**

**so the length can be 3cm, 15.44cm, or 1.55cm?**