Here is a small tip from my side,
whenever u get to find a TSA or CSA or VOLUME of a combination of solids,  do not find each one separately and then add or subtract or whatever.Stop without actually calculating that is just substitute and then solve at last so that u can di easy calculation by taking the commom term or using identities.(not in all the cases)
You firstly read the problem ...
then to calculate simply you have to take common from the formula...

if you have to say tha find the TSA of combind figure then you have to take the CSA of both figure
and if you have to say that find the capacity of the solid then you have to take volume formula