labor

hi. any suggestions how I can track labor when i sell things. for instance i sell a widget and i need a tech to spend 3 hours building it . when i sell 10 widgets I want to be able to see that i had 3 x 10 hours labor =30 hours. this way i can determin which staff person is the most efficient. so if i allow him 30 hours , but he only actually spends 20 hours , he is elegable for a bonus.