Where is the "Upper end of 95 percent range" and "Upper end of 68 percent range" coming from?; I still don't understand how to interpret the answer

TB MC Qu. 12-75 A stock had annual returns of... A stock had annual returns of 5.3 percent, -2.7 percent, 16.2 percent, and 13.6 percent over the past four years. Which one of the following best describes the probability that this stock will produce a return of 20 percent or more in a single year? Multiple Choice Less than 2.5 percent but more than 5 percent More than 16 percent Less than.5 percent Less than 1 percent but more than .5 percent Less than 16 percent but more than 2.5 percent Explanation Average return = (.053 - .027 +.162 + .136)/4 Average return = .081, or 8.1% o = {[1/(4 - 1)] [(.053 - .081)2 + (-.027 - .081)2 + (.162 - .081)2 + (-136 - .081)213.5 0 = .0857, or 8.57 percent Upper end of 95 percent range = .081 + 2 (0857) Upper end of 95 percent range = .2524, or 25.24% Upper end of 68 percent range = .081 +.0857 Upper end of 68 percent range = 1667, or 16.67% A return of 20 percent or more in a single year has less than a 16 percent but more than a 2.5 percent chance of occurring