Inserting A Total Amount Field In Each Empty Row

to run a macro that enters a new row after each set of currencies (which have been sorted). I now need to enter a total balance cell within this empty row which calculates the total amount for each currency.

I need to do this using the SUMIF function below:
SUMIF($J$3:$J$300,"L/C",$I$3:$I$300)-SUMIF($J$3:$J$300,"L/D",$I$3:$I$300)

the above basically lets me calculate the total but as no - and + signs were input it does this by recognising the 'dr' and 'cr' in the column next to the amount.