Chem assignment help! I did something wrong and I could really use some explanation as to how to do this question?

For the equation 4Cl2 + H2S + 4H2O —> H2SO4 + 8HCl, if 20,000L of contaminated water was in a tank with a concentration of hydrogen Sulfide of 7.13 x10-4, what volume of chlorine at STP is required to remove all hydrogen sulfide from the water?
4 answers 4