Not perform sum if cell is blank

Hello,

I have the spreadsheet attached. The problem is that I only want data to show in the cells where the sum is complete (and the result is 70). I don't want there to be anything in the cells where one of the cells involved in the sum was blank (I currently get 0, 20 or 50 in these cells). Is there a formula I can do for this?

And if so, is there a simple way of adding it into all cells, or will I have to manually add it to them?

Thank you in advance for any assistance anyone can give.

Example.xlsx

In C3, then drag across

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Ah thanks for the help but I wasn't quite clear. This is an example - in my actual workbook there could be any number in the cell (it's not always 70). I'm looking for a formula that says not to perform the sum if one of the cells involved in the cell is blank.

That, Glenn, is perfect! Thank you enormously!