I hope that this is a fairly straightforward way to show the calculations for working out surface area and volume of a cuboid cell, and then putting the two together to show the all-important surface area to volume ratio. Volume increases faster than surface area, thus the ratio of the two (SA : Vol) becomes smaller and smaller.
SOLUTIONS TO THIS PROBLEM FOR CELLS?
Create a convoluted or highly irregular surface area
I have tried to create the typical boxes which IB uses, inside which you should answer the questions. The necessary skill here is PLANNING and MORE PLANNING, so that what you eventually write is not coming straight and immediately out of your head but is prepared. Work on it!