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?