The products of an agricultural firm are delivered by four different transportation companies, A, B, C, and D. Company A transports 40% of the products; company B, 30%; company C, 20%; and finally, company D, 10%. During transportation, 5%, 4%, 2%, and 1% of the products spoil with companies A, B, C, and D, respectively. (a) If one is randomly selected, obtain the probability that it is spoiled. (b) If a product is spoiled, derive the probability that it has been transported by company A.