(i) Well if there's 5% of the total mass being stibnite, that means there is:
0.05 x 500,000 = 25,000g of Sb2S3
Then you should be able to use the moles = mass/mr to solve that.
(ii) Using the answer from the previous question, and looking at the molar ratio from the balanced equation, you can use the same 'mole' formula to work out how much antimony can be formed..
Does that help?