Bangalore dairy sales Milk in two kinds of packets: Plastic Bag $\&$ Tetra Packs. Each of these packets goes through three steps: Filling, Sealing and Labelling. The company has three filling machines, 6 sealing machines and 3 labelling machines. Each of these 12 machines can work for exactly 8 hours in a day. One box of Tetra Packs requires 20 minutes for filling, 1 hour for sealing and 20 minutes for Labelling. The box of Plastic Bags requires 15 minutes for filling, 1 hour for sealing and 10 minutes for labelling. If the dairy has to manufacture only 40 boxes of Tetra Packs then how many machine hours are utilised on that day?