Cynthia Knott's oyster bar buys fresh Louisiana oysters for $4 per pound and sells them for $9 per pound. Any oysters not sold that day are sold to her cousin, who has a nearby grocery store, for $2 per pound. What is Cynthia's profit per pound on the oysters sold to her cousin?
a) $2
b) $3
c) $5
d) $7