Question

Suppose that there is a white urn containing two white balls and one red ball and there is a red urn containing one white ball and three red balls. An experiment consists of selecting at random a ball from the white urn and then (without replacing the first ball) selecting at random a ball from the urn having the color of the first ball. Find the probability that the second ball is red.

I need someone to explain to me how to do this step by step.