Consider a four-step serial process with processing times given in the following list. There is one machine at each step of the process, and this is a machine-paced process. 

• Step 1: 25 minutes per unit 
• Step 2: 15 minutes per unit 
• Step 3: 30 minutes per unit 
• Step 4: 20 minutes per unit 

Assuming that the process starts out empty, how long will it take (in hours) to complete a batch of 105 units?