Construct a 90 % confidence interval for the standard deviation of costs.

An automobile manufacturer wants to study the repair record of its own cars. The performance of 1,000 cars and their maintenance records were monitored after they were sold to consumers. In a span of 3 years, 3,560 repairs occurred among the 1,000 cars monitored. The standard deviation of the number of repairs for 1 car is 2.5. A total of $303,000 was spent to repair the cars. The standard deviation of repair costs for 1 car is $60. There are 205 cars that did not have any repairs in the 3 years.