Question

What is the surface area of a cube if there are widths of 3.1

Answer 1

This makes no sense. What widths? Do you mean edges?

Cube Volume = Edge^3

Cube Surface Area = 6 * Edge^2

These are known formulas. You should memorize them

Answer 2

A cube has a side length.
A cube is similar to a rectangular prism, that we dealt with before, but in a cube, all 6 faces have the same area.

All side lengths in a cube are equal, so if you are given the side length, that side length is both the length and width of each face.
Find the area of one face, and multiply by 6 to find the total surface area.