Quick Start Company makes 12-volt car batteries. After many years of product testing, the company knows that the average life of a Quick Start battery is normally distributed, with a mean of 45.0 months and a standard deviation of 5.7 months.

If Quick Start does not want to make refunds for more than 10% of its batteries under the full-refund guarantee policy, for

how long should the company guarantee the batteries (to the nearest month)?