Do you want the conditional format formula?
If there are only two cells D5 and C5 compared, you may refer to the formula:
=$D$5>$C$5*0.1, and set the font to be red.
If there are multiple rows of cells in C column and D column to be compared, you may try formula:
=$D5>$C5*0.1, and apply the formula to the cells in D column, set red for their font.
Any misunderstandings, please feel free to let me know.
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