A parallel plate capacitor has plate area a = 405 cm2 and an air-filled gap between the plates that is 2. 25 mm thick. The capacitor is charged by a battery to 575 v and is then disconnected from the battery. How much energy is stored in the capacitor?.

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.