Stuck on homework problem for chemistry it’s due tonight

Question

You are trying to determine the concentration of a stock solution of hydrochloric acid. You have 450.80 mL of 0.86 M dilute solution that was prepared with 25.50 of stock solution.

Answer 1

The most direct way to do this is to realize that the Molarity x the volume before dilution = the Molarity x the volume after dilution. (M V)_before = (M V)_after

Since you know the molarity & Volume of the diluted (after) solution, and the volume of the more concentrated solution, you can solve for M_before