Host A
Host A composes its data at the Application layer, and then encapsulates that data in a Transport layer protocol.
The data frame is passed to the Internetwork layer where the IP address (192.168.4.22) for Host B is added.
Since Host A is communicating with a remote host, it uses the MAC address of its default gateway (Router 1) when encapsulating the data frame at the Network Interface layer.
Once Host A has properly composed, formatted, and addressed the packet, it transmits the packet on the network.
The other hosts on the network (Q and X) receive and discard the packet because the MAC address does not match theirs.
Router 1 accepts the packet because the MAC address matches.