yes I doso 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- 80gCr-52gO-64gsince 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!