Mrs. johnson has 10 blue pens, 14 black pens, and 4 red pens in a desk drawer. if she selects two pens at random without replacing them, what is the probability that she selects a red pen and then a black pen?

There is a total of 28 pens 
probability of first getting a red pen is 4/28 or 1/7
probability of second getting black pen is 14/27 cuz one pen was already removed and not replaced so 28-1=27 
multiply 1/7 with 14/27 and you get the answer

(-14+3/2b) - (1+8/2b) = -5 -5/2b(-10+b) + (7b-5) = 8b-15(7/2b-3) - (8+6b) = -5/2b-11(5+2b) + (2b+3/2) = 4b+ 13/2