Two taps a and b fill a swimming pool together in two hours. alone, it takes tap a three hours less than b to fill the same pool. how many hours does it take each tap to fill the pool separately?

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