<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_actual_replica(self, service_id: str) -> str: """Get the actual replica level of a service. Args: service_id (str):
 docker swarm service id Returns: str, replicated level of the service """

        # Raise an exception if we are not a manager
        if not self._manager:
            raise RuntimeError('Only the Swarm manager node can retrieve '
                               'replication level of the service')

        service_details = self.get_service_details(service_id)
        actual_replica = service_details["Spec"]["Mode"][
            "Replicated"]["Replicas"]
        return actual_replica