4. I've always wanted to own biased (or "loaded") dice, so I bought a triplet that I found on Amazon. According to the manufacturer, each die is biased to roll a "six" 75% of the time. (a) (2 points) If I roll a single die over and over until I get a "six", how many rolls will it take on average? (b) (2 points) If I roll all three dice, what is the probability that I get at least one 6? ' (c) (2 points) If I roll all three dice, what is the probability of getting exactly three 6's