Let A be the first brand and B the second brand, then, we can write
[tex]\begin{gathered} 0.05A+0.08B=0.06\times300\ldots(a) \\ \text{and} \\ A+B=300\ldots(b) \end{gathered}[/tex]so we have 2 equations in 2 unknows.
Solving by substitution method.
By moving B to the right hand side in the second equation, we have
[tex]A=300-B\ldots(c)[/tex]By substituting this result into equation (a), we have
[tex]0.05(300-B)+0.008B=18[/tex]where 18 = 0.06x300. By combining similar terms, we get
[tex]\begin{gathered} 15-0.05B+0.08B=18 \\ 15+0.03B=18 \end{gathered}[/tex]By moving 15 to the right hand side, we obtain
[tex]\begin{gathered} 0.03B=18-15 \\ 0.03B=3 \end{gathered}[/tex]then, B is equal to
[tex]\begin{gathered} B=\frac{3}{0.03} \\ B=100 \end{gathered}[/tex]Now, by substituting this result into equation (c), we have
[tex]\begin{gathered} A=300-100 \\ A=200 \end{gathered}[/tex]This implies tha the answer is:
First brand: 200 mililiters
Second brand: 100 mililiters