VLOOKUP Problem formula not vba

[ukdane]

xld: In your example: =INDEX(L1:L3,MATCH(2.5,K1:K3,-1))

I don't know what the index is exactly, as it is generated by another cell.
For example, the formula could read:

=INDEX(L1:L3,MATCH(2.5,K1:K3,-1))
=INDEX(M1:M3,MATCH(2.5,K1:K3,-1))
=INDEX(N1:N3,MATCH(2.5,K1:K3,-1))

based on the results of another lookup table elsewhere, that returns either L, M, or N.
How do I add the L, M, or N to where I've placed the X below?

=INDEX(X1:X3,MATCH(2.5,K1:K3,-1))

(Just to make it even more complicated, X is on another worksheet).

Cheers