Question on H2O2 drops:

Say I wanted to ass 1 drop of 35% H2O2 to 8 oz of CS.  Is this is the same
as putting about 11 or 12 drops as 3% H2O2 (i.e. 35 divided by 3)?  Also,
does it need to be food grade, or is the stuff form walgreen's okay?

Thanks,
~David