A data processing task is distributed across four worker nodes. For a specific computational step, all nodes must finish their work and exchange results before any node can proceed to the next step. The completion times for this single step on each node were measured as follows:

• Node 1: 8 seconds
• Node 2: 10 seconds
• Node 3: 8 seconds
• Node 4: 12 seconds

Identify the total time required to complete this single computational step for the entire system and explain why the system's overall performance is not simply the average of the individual node completion times.