Question 710351
This one is the same general problem as question #710342.  Different materails, different mixture unit, different values; but the same problem.


VARIABLES
High concentration fertilizer percent, H =52%
Low concentration fertilizer percent, L =22%
Target percent wanted, T = 42%
Amount of High conce. to use, v
Amount of Low conce. to use, u
Amount of target mixture produced, M = 90 Liters


This system can be formed from the description and question
{{{(uL+vH)/M=T}}}
{{{u+v=M}}}


If we use the second equation as {{{v=M-u}}}, we can substitute it into the rational equation and solve that one for u, giving us this:
{{{highlight(u=(M(T-H))/(L-H))}}}


Now, just substitute the values and compute u.
We can then go to our simpler-looking expression for v and find (compute) it, too.  {{{highlight(v=M-u)}}}