we calculate the vinegar on 220 ml
the dressing will have 15.4 ml of vinegar
now we can raise a sum
where X is the first brand and Y the second brand on ml
now the percent vinegar sum we know the result is 15.4 wich corresponds to 7%
we have two unknowns and equations, so we can solve by any method.
i will solve y on the first equation
and replace on the second to find x
then replace x on any equation to solve y
for each brand should she use x=176ml and y=44ml