To help fill its seats for a particular flight, an airline offers a special nonrefundable fare of $200 for customers who make a reservation at least 21 days in advance and satisfy other restrictions. Thereafter, the fare will be $600. A total of 100 reservations will be accepted. The number of customers who have requested a reservation at full fare for this flight in the past always has a normal distribution with mean 40 and standard deviation 10. Determine how many seats should be reserved for customers who pay full fare.