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. So plus x times ten to the 6th or 1 million. We do a little bit of simple algebra to solve for x, we divide through by ten to the six we get 90,000 divided by 1 million equals this guy. Now, we multiply through by 450 plus x and we get 0.9, which is simply this guy times 450 plus x equals the x was left over on that side, so equals x.