Not sure how to balance this out. please help

Question

A chef is going to use a mixture of two brands of Italian dressing. The first brand contains 7% vinegar, and the second brand contains 12% vinegar. The chef wants to make 340 milliliters of a dressing that is 8% vinegar. How much of each brand should she use?

Answer 1

Look at the vinegar concentrations.

In 1st dressing we have  .07x ml

In 2nd dressing we have .12(340-x) ml

The total should be .08(340)

 

.07x + .12(340-x) = .08(340)

multiply by 100

7x + 12(340-x) = 8(340)

7x + 4080 - 12x = 2720

 

Finish solving for x to find out how many ml of 7% vinegar dressing to use.

Then 340 - x is how many ml of 12% vinegar dressing to use.