A child is 40 inches tall, which places her at the 90th percentile of all children of similar age. The heights for children of this age form an approximately Normal distribution with a mean of 38 inches. Based on this information, what is the standard deviation of the heights of all children of this age?

(a) 0.20 inches

(c) 0.65 inches

(e) 1.56 inches

(b) 0.31 inches

(d) 1.21 inches