What is the difference of (1 - i) and (-7 * 31)

According to the article, which five aspects of mindfulness did researchers study?

Consider the image seen here. the image, at point y, represents the process of during which a is being produced.

Raul has one solution that is 20% acid by volume and one solution that is 50% acid by volume. he plans to mix together some of each solution to create 30 milliliters of a solution that is 40% acid by volume. how many milliliters of the 20% acid solution should raul use to create the 40% acid solution? can someone explain this to me? i know that the answer is 10 milliliters, but i don't know how to get it.