Solution:
Let us denote by x the milliliters of 9% vinegar to be used in the mixture. Then, the following amount
[tex]340\text{ - }x\text{ }[/tex]is the number of milliliters of 14% vinegar to be used in the mixture.
Taking this into account, we obtain the following equation:
[tex]0.09\text{ x }+0.14(340-x)=0.12(340)\text{ }[/tex]this is equivalent to:
[tex]0.09\text{ x -0.14 x + 47.6 = 40.8}[/tex]this is equivalent to:
[tex]-0.05\text{ x = -6.8}[/tex]or
[tex]0.05x\text{ = 6.8}[/tex]solving for x, we get:
[tex]x\text{ = }\frac{6.8}{0.05}=\text{ 136}[/tex]so that, the correct answer is:
ml of 9% vinegar to be used in mixture= 136 ml
ml of 14% vinegar to be used in mixture = 340 ml - 136 ml = 204 ml