The problem asks to calculate the surface area of a cube with a side length of 6 units.

The formula for the surface area $A$ of a cube is: $A = 6 \times s^2$ where $s$ is the length of one side of the cube.

Given that $s = 6$: $A = 6 \times (6)^2 = 6 \times 36 = 216$

Therefore, the correct surface area is 216 square units.

Do you need more details about surface area calculations or have other questions related to this? Here are a few suggestions to explore:

1. How does the surface area of a cube compare to that of a sphere?
2. What happens to the surface area if the side length of the cube is doubled?
3. How do you calculate the volume of a cube?
4. Can surface area be calculated for irregular shapes? How?
5. How does the surface area relate to real-world applications like packaging?

Tip: When solving geometry problems, always remember that cubes have equal side lengths, and all faces are squares.