How to create Calculated field to SUM in Report Designer?

I have created additional column in transactions details, I sum all columns at bottom 

In report format, I sum for total Labour Cost, Total Material Cost and Total Other Cost, however, I want to create a Total Cost at the bottom. How should I create it?   

Solution : 

Step 1 :Field List à QuotatinDetailsCollection à Right Click à  Add Calculated 

Step 2 : Enter Display Name and set Field Type as Decimal 

Step 3 :  set Expression as [Quotation Details Collection][].Sum([Total Lab] + [Total Mat])  + [TotalEstOtherCost]

Please refer attachment