V Look up explanation

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=IF(E10<>"",IF(L10="M",VLOOKUP(E10,CostTable,2),IF(L10="R",VLOOKUP(T10,RepairCost,2),IF(L10="C",VLOOKUP(E10,CleanTable,3),"??"))))
1st part...
=IF(E10<>"",
IF E10 contains anything (is not blank)

IF(L10="M",VLOOKUP(E10,CostTable,2),
IF L10 contains M, find the contents of E10 in the table called CostTable, and return the value in the 2nd column

IF(L10="R",VLOOKUP(T10,RepairCost,2),
If L10 does not contain M, but instead, contains R, find the contents of T10 in the table called REpairCost, return the value in the 2nd column

IF(L10="C",VLOOKUP(E10,CleanTable,3),
else if L10 = C, then same process for CleanTable

"??"))))
If none of these match, put ?? in te cell as the answer