Miio the answer is C
slightly complicated but
we have the original cube with TSA = m
then we split it in half, and you get the TSA of the original cube, + the two cross-sections from the area you just cut (which is 2n)
so TSA is m + 2n
next you do the same thing, but horizontally
so if you visualise it you have 2 more cross-sections of area n each, so your final TSA is m + 4n
hence you have an increase from m to m + 4n so your answer is C
im working on a document with solutions to the questions atm
