Sammy's is the hot new lunch spot among the hipsters, who flock there at noon for their artisanal peanut butter and jelly sandwiches, which sell for $12.95. The sandwiches are made from two slices of their own artisanal bread, which they bake continuously throughout the day at a rate of seven loaves an hour (each loaf contains twenty slices). The actual cost of a loaf of bread is $1 and the cost to hold a loaf is 80%, since freshness is important in baking as well as to hipsters. The cost to run a new batch of a dough is $3 per loaf. Sammy's sells their sandwiches at a rate of fifty per hour. What is the optimal batch size to produce?