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 $\displaystyle 588cm^3$. 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**

**$\displaystyle 4x^3-80x^2+400x-588=0$**

**$\displaystyle 4(x^3-20x^2+100x-147)=0$**

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

**and was left with $\displaystyle x^2-17x+49$**

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

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