I never took Stats before, so I'm just trying to get a grasp of statistics and make sure I understand all of it.

A box in a certain supply room contains four 40-W lightbulbs, five 60-W bulbs, and six 75-W bulbs. Suppose that three bulbs are randomly selected.

(c) What is the probability that one bulb of each type is selected?

(d) Suppose now that bulbs are to be selected one by one until a 75-W bulb is found. What is the probability that it is necessary to examine at least six bulbs?

Hope I did these right! Part d is especially tricky so I wouldn't be surprised if I tripped over on that one.