8. A running back in the National Football League plays for an average of 4 years with a standard deviation of. 0.5 year. Assuming the playing times to be approximately bell-shaped. Using the Empirical Rule (i) what percent and (ii) how many of running backs who play (a) more than 3.5 years; (b) less than 4.0 years; (c) between 2.5 and 5.0 years