yes I do
so u need to find the amount of grams total and the individual amount of grams.
so 40+40+52+16+16+16+16=196g (I got the numbers from the periodic table)
K- 80g
Cr-52g
O-64g
since you are solving for oxygen, you would only use the oxygen part so...
64g/196g=32.9%
32.9% is the answer
hope this helps! if it doesn't, let me know in the comments! have a blessed day!