A substance contains 35.0g nitrogen, 5.05g hydrogen, and 60.0g oxygen. How many grams of oxygen are there in a 200g sample of the substance?
Add up the masses of N,H and O to find the mass of the compound = 100.05 grams
You then know that this mass of the compound contains 5.05g of hydrogen.
So by proportion, you can find how much hydrogen will be in 200g of the compound
100.05 grams of the compound contains 5.05g hydrogen
200g of the compound contains (5.05/100.05)×200g
=10.1