How do you solve this?

Need ! easy 6th grade work! i will put as much points as i can! you so much! i’m learning this in math and it’s soo

Don't know how to find x given these segment lengths

Abag contains 4 red, 7 blue and 5 yellow marbles. event a is defined as drawing a yellow marble on the first draw and event b is defined as drawing a blue marble on the second draw. if two marbles are drawn from the bag, one after the other and not replaced, what is p(b|a) expressed in simplest form? a. 7/16 b. 7/15 c. 14/16 d. 14/15