Which is the least profitable investment for a candy shop that earns a $1 profit per pound of candy?

Which is the least profitable investment for a candy shop that earns a $1 profit per pound of candy? worker at $10 per hour, producing 8 pounds of candy per hour worker at $12 per hour, producing 16 pounds of candy per hour machine with $5 per hour operating cost, producing 10 pounds of candy per hour machine with $8 per hour operating cost, producing 14 pounds of candy per hour