how to get totals of sales order and purchase order

  public real SalesTotal(str salesId)

    {

        SalesTotals salesTotals;

        SalesTable salesTable;

        SalesLine salesLine;

        TaxAmountCur salesAmt, taxAmount, amt1, discountAmt, totcharges, totOfOrder,                      contributionRatio;

        Tax tax;

        salesTable = SalesTable::find(salesId);   //give sales id here 

        salesLine = SalesLine::find(salesTable.SalesId);

        salesTotals = SalesTotals::construct(salesTable);

        tax = Tax::construct(NoYes::No);

        salesAmt    = salesTotals.totalBalance();

        taxAmount   = salesTotals.totalTaxAmount();

        discountAmt = salesTotals.totalEndDisc();

        totcharges  = salesTotals.totalMarkup();

        totOfOrder  = salesTotals.totalAmount();

        contributionRatio   = salesTotals.totalContributionRatio();

        info(Strfmt("Invoice Amount %1",totOfOrder ));

        return totOfOrder;

    }