The 40 ml solution is said to be created from 10 ml and 30 ml solutions. In mixture problems, we equate the final mixture to its compositions given the concentration for each. A 10 ml has 20% acid and the 30 ml has C (unknown). We can write the total liters for 10 ml as 10(.2) and 30(c) for the 30 ml. when two solutions were added, it should be equal to 40ml with 32% acid. Therefore, it should be written as 10(.2) + 30(c) = 40(.32). The answer is A
