Last year I created a spreadsheet with the following formula:
=IF(ISBLANK(B20),"",B20*$E$9) entered under the services
NOTE cell E9 = 600
<tbody>
Qty
Service
Expenses
Total
1
600
20
620
</tbody>
=IF(OR(ISBLANK(B20)),"",(D20+E20)) entered under Total
OK this has worked until I upgraded...