Question 992563
u gallons of Brand B, 20%
v gallons of Brand A, 50%


{{{system((20u+50v)/6=40,u+v=6)}}}
and solve the system for u and v.


You can also do the problem in just one variable if you use the method like in this example:
<a href="https://www.youtube.com/watch?v=-REjxT9KCzQ">two-part mixture with just one variable</a>