How to check if one of the fields in a formula is empty and color the cell if it is empty?

Question

Google Sheets

I have, say, 4 cells. In 4, the result of the calculation of the three previous cells is displayed. How can I color this 4th cell red if, for example, 2nd cell is empty? Only 2 cells can be empty. It is necessary to paint 4 - with the result.

Answer 1

Answer 2

Easily!
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