The equation to find P(A and B) is P(A and B)= P(A) x P(B/A). P(B/A) stands for probability of B given A. First we need to find out the P(A). The P(A) is 8/13 because you have 13 marbles total and 8 white marbles. For P(B/A), it is 5/12. This is because there are 5 red marbles and given that A happened, there would only be 12 marbles left in the bag, leaving you with a 5/12 chance of getting a red marble. Now plug it in. 8/13 x 5/12 = 40/156, which simplifies down to 10/39. Thus, B is the answer.