J.J. Kettering & Associates is a financial planning group in Fresno, California. The company specializes in financial planning for schoolteachers in the Fresno area. As such, it administers a 403(b) tax shelter annuity program in which public schoolteachers can participate. The teachers can contribute up to $20,000 per year on a pretax basis to the 403(b) account. Very few teachers have incomes sufficient to allow them to make the maximum contribution. The lead analyst at J.J. Kettering & Associates has recently analyzed the company's 403(b) clients and determined that the annual contribution is approximately normally distributed with a mean equal to $6,400. Further, he has determined that the probability a customer will contribute over $13,000 is 0.025. Based on this information, what is the standard deviation of contributions to the 403(b) program?