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

worker at $10 per hour, producing eight 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