On the network shown in the figure, all switches run STP.

The root path cost (RPC) of a switch is the total path cost from that switch to the root bridge along the selected spanning-tree path. Since SW1 is given as the root bridge, its RPC is 0. Each link in the topology has a path cost of 20. To determine SW4’s RPC, you identify the shortest active STP path from SW4 to SW1.

Based on the topology used in the question, SW4 reaches SW1 through a path containing two links. Therefore, the total root path cost is 20 + 20 = 40, which makes option B correct. This is a standard STP calculation. HCIA-Datacom uses RPC as one of the main comparison parameters in root-port election on non-root switches. A lower RPC means a better path toward the root bridge. If multiple candidate ports have the same RPC, the switch then compares the sender’s bridge ID and port ID. This question checks whether the learner understands that RPC is cumulative across the spanning-tree forwarding path and is not simply the cost of a single directly connected link unless the switch is directly attached to the root bridge.