Question 968220
<a href="http://www.algebra.com/my/Mixtures%3A-All-in-Symbols.lesson?content_action=show_dev">Mixing two concentrations for known amount of mixture </a>
http://www.algebra.com/my/Mixtures%3A-All-in-Symbols.lesson?content_action=show_dev


You should try, instead of what shown in that lesson, to use only a single variable to solve this mixture problem.  Either way, you can still study and use the referenced lesson.