Four customers per minute enter the Frugal Fast Food restaurant during lunch hour and spend an average of 4 minutes getting their food (in a queue and reƧeiving service). After receiving their food, $40 \%$ of the customers leave the restaurant (with their food) while $60 \%$ remain to eat their food inside Frugal Fast Food. Those who stay spend an average of 25 minutes consuming their food. How many customers are inside Frugal Fast Food during the lunch hour, on the average?