Achef is going to use a mixture of two brands of italian dressing. the first brand contains 9% vinegar, and the second brand contains 14% vinegar. the chef wants to make 240 milliliters of a dressing that is 13% vinegar. how much of each brand should he use

Let the amount of the first brand be x, and let the amount of the second brand be y.
0.09x + 0.14y = 240 * 0.13 .................(1)
x + y = 240 ..............(2)
y = 240 - x .......................(3)
Plugging the value for y from equation (3) into equation (1), we get:
...............(4)
Equation (4) simplifies to:
-0.05x = -2.4
giving the value for the required amount of 9% vinegar as 48 ml and the required amount of 14% vinegar as 240 - 48 = 192 ml.