A formula that adds 12 to a text value to give a text value in return

I have been using the formula you guys supplied me with and it works like a dream but in the last part of my spreadsheet I have to change the formula slightly.

I need to add the value of 12 to a cell (CP5) but get the answer displayed as text again e.g. 1a, 1b etc. Any ideas, im sure its a simple fix??

How do i ammend the following??

=LOOKUP(CP5,{"1a","1b","1c","2a","2b","2c","3a","3b","3c","4a","4b","4c","5a","5b","5c","w"},{11,9,7 ,17,15,13,23,21,19,29,27,25,35,33,31,3})


Andy