the amounts of the 1st and 2nd solution, will be 300 + 600, or 900 liters
the amount of pure soap in the solution will be (0.30)(600)+(0.60)(300)
thus whatever (0.30)(600)+(0.60)(300) is, must equal 900x, since that's how much pure soap the mixture of 900liters has
[tex]\bf \begin{array}{lccclll}
&amount&soap&\textit{amount of soap}\\
&-----&-----&--------\\
\textit{first solution}&600&0.30&(0.30)(600)\\
\textit{second solution}&300&0.60&(0.60)(300)\\
-----&-----&-----&--------\\
mixture&900&x&(900)(x)
\end{array}\\\\
-----------------------------\\\\
(0.30)(600)+(0.60)(300)=(900)(x)[/tex]
solve for "x"
