Acube has a surface area of 486 cm2. what is the side length ?

A Cube, has all equal sides, namely, the length, width and height
are all equal to each other

so..  notice the picture added here
you have really, 6 squares, stacked up to each other at the edges

so...what is the Area of one of those squares?
well, if the sides are equal, let's say the side is "x" long, then
the Area is 

well, you have 6 of those squares, thus 

solve for "x", to get one side's length

Look at this and see if it