Question

which of the following is the surface area of a cube with a side length of 9cm

Answer 1

Area= 6a^2
6times 9^2
486 cm^2

Answer 2

one may note, you're missing info in your posting

but in any case, notice the picture below, a cube has all sides equal, and notice, is just 6 rectangles stacked up at the edges, and each is a 6x6