Answer:
21 cm
Step-by-step explanation:
You know the volume is 486 cm^3
The height for the box is 6 cm
The length and the width equal each other (because it's a square)
We can call the length and the width "x"
The volume of a box equals V=lwh
Now we can substitute
486=6*x*x
486=6x^2
81=x^2
x=9 or -9
x cannot be -9 because dimensions cannot be negative
Now we have to add 9+6+6 to find the whole side of the original square (before the 6x6 sqares were cut out)
9+6+6=21