A company's manufacturing process uses 500 gallons of water at a time. A "scrubbing" machine then removes most of a chemical pollutant before pumping the water into a nearby lake. To meet federal regulations the treated water must not contain more than 80 parts per million (ppm) of the chemical. Because a fine is charged if regulations are not met, the company sets the machine to attain an average of 75 ppm in the treated water. The machine's output can be described by a normal model with standard deviation 4.2 ppm. What percent of the batches of water discharged exceed the 80 ppm standard? Laptop computers have been growing in popularity according to a recent study. Laptops now represent more than half the computer sales in a certain country. A campus bookstore sells both types computers and in the last semester sold 60% laptops and 40% desktops. Reliability rates for the two types of machines are quite different, however. In the first year, 6% of desktops require service while 17% of laptops have problems requiring service. Complete parts a through c below. a) Sketch a probability tree for this situation. Laptop Desktop (Type integers or decimals.) Requires service -Does not require service Requires service -Does not require service b) What percentage of computers sold by the bookstore last semester required service? Of all the computers sold by the bookstore, % of them required service. (Type an integer or a decimal.) c) Given that a computer required service, what is the probability that it was a laptop? Given that the computer required service, the probability that it was a laptop is (Round to four decimal places as needed.)