For the Data Validation, create a list of all the sources available and make it a Named Range. I put it in column T in the attached.
You can make the list Dynamic (DNR), so that you can add and remove sources at will.
Go to Formulas tab, then Define Name from the Defined Names section, then enter a name like: Sources and apply formula: =OFFSET(Sheet1!$T$1,1,0,COUNTA(Sheet1!$T:$T)-1,1) click Ok to accept
Now select G3:G6 and go to Data|Validation and select List from the Allow menu, then apply formula: =Sources
Finally, in L3 apply formula:
=IFERROR(INDEX(B:B,MATCH($G3,$A:$A,0))*$J3/100,0)
copied across and down the table.
Now make selections, enter amounts and see the results.
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