Calculated Field to divide amount by total and multiple by number

As you are using the 365 version of Excel you could use Power Pivot.
1. Convert A1:B6 into a table
2. Add the table to the Data Model and then add a column (Total) populated using: =sum(Table1[Amount])
3. Add a measure Formula:=SUM(Table1[Amount])/AVERAGE(Table1[Total])*5
4. Produce a pivot table from the data model put Category in the Rows area then Amount and Formula in the Values area.
Note that Formula is formatted through the Data Model.
Let us know if you have any questions.