Consider the molar volumes of He , Ar, H2, and N2 Listed in table 2 at 323 K. what is the order of these gases from the gas having the smallest molar volume to the gas having the largest molar volume?

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.