South Trucking, Inc. stock is expected to return 8.4 percent in a boom, 8.9 percent in a normal economy, and 9.2 percent in a recession. The probabilities of a boom, normal economy, and a recession are 6 percent, 92 percent, and 2 percent, respectively. What is the standard deviation of the returns on this stock? (round to six decimal places for intermediate calculation) .06 percent 13 percent .42 percent .38 percent .55 percent