I am writing a research report and would like to know how to calculate the standard deviation of reduction %.

The data of 24 hours is "control: 1.117 SD1; 10 uM curcumin: 0.947 SD2",

and we want to say "Compared to the negative control, cells treated by 10 M showed a drop in proliferation of 15.2% SD {(1.117 - 0.947)/1.117 = 15.2% } after 24 hours", how should we calculate the SD of the 15.2% drop in these two groups of data?