Question 934974
Initially the mixture is 7 parts.  The final mixture can be understood of 9 parts, although
the parts will become different size.


Concentration of milk at start is {{{5/7}}}, and concentration of milk wanted is {{{4/9}}}.
Simple two-part mixture problem.


Let x be how many parts milk to add to the start mixture.
{{{highlight((56(5/7)+x)/(x+56)=4/9)}}}.
Solve for x, the liters of milk to add.