Try the following...

=INDEX('Bath Tissue'!R3C1:R12C18,MATCH('DVoid Import Sheet'!RC9,'Bath Tissue'!R3C1:R12C1,0),CHOOSE(MATCH(RC15,{36,32,28,24,20},0),4,5,6,7,8))

OR

=INDEX('Bath Tissue'!R3C1:R12C18,MATCH('DVoid Import Sheet'!RC9,'Bath Tissue'!R3C1:R12C1,0),VLOOKUP(RC15,Sheet3!R1C1:R5C2,2,0))

...where Sheet3!R1C1:R5C2 contains the following table:

36	4
32	5
28	6
24	7
20	8
I'm assuming that the reference for the first INDEX function should be R12C18 not R12C15.

Hope this helps!