So 18 grams/mol times 25 moles gives you 450. Now, moles cancel, the grams are left, so we have 450 grams of H 20. Now, we want to find the amount of HCL we need to add in terms of grams to create a 90,000 parts per million solution. So we simply use the parts per million formula. We say, well, we want to create a 90,000 grams or parts per million solution equals x is the amount of HCL grams we need to add divided by the total amount of grounds we have the solution. So we already have 450 grams of water plus the amount of HCL and grounds we will add.