Question 1024723
This explains how that general question works:


<a href="https://www.algebra.com/my/Mixtures%3A-All-in-Symbols.lesson?content_action=show_dev">Mixing two concentrations for known amount of mixture </a>


Reason for the lesson is because they ALL work that way, so learn to solve one of them and you know how to do all of them.  The general solution for this type is also shown.