Change query source with a parameter

I'm trying to change the data source of a query using a parameter, but I can't figure out the correct syntax. Here's my query:

let
    Source = OleDb.DataSource("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\Temp\;extended properties=dBASE IV", [Query="select * from [JunctOut.dbf]"])
in
    Source

I want to be able to change the data source to a different path (currently C:\Temp\ in the example above). I've created a parameter called FolderPath, but can't figure out how to get it into my query. 

Any suggestions?