Answer :
Andrew has 8 blue marbles, 6 red, and 10 green.
8+6+10 = 24 marbles in total.
If he selects a marble, replaces it in the bag, and then selects another, we're being asked the probability that the first marble is blue and the second is red.
You have a 6/24 (1/4) chance of the first one being red.
So you have a 8/24 (1/3) chance of the second being blue.
Since replacement occurs, we multiply them together:
1/4 * 1/3 = 1/12.