passing a variable to a report form

Hello.

I have a webform that when the user clicks print receipt, it will print a report. This works ok. But l want to pass a variable from the form to be displayed in the report.

My code so far: I want to pass totalcost and display that in the report.

Code:

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string totalCost = "1000";
                        rptReceipt customerReceipt = new rptReceipt();
                        this.rptViewerReceipt.SelectionFormula = "{PurchasedProducts.CustomerID} = '" + customerID + "' ";
                        this.rptViewerReceipt.ReportSource = customerReceipt;
                        this.rptViewerReceipt.Refresh();
                        this.rptViewerReceipt.Show();

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Many thanks in advance,

Steve