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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _find_usage_instances(self):
 """find usage for DB Instances and related limits"""

        paginator = self.conn.get_paginator('describe_db_instances')
        for page in paginator.paginate():
            for instance in page['DBInstances']:
                self.limits['Read replicas per master']._add_current_usage(
                    len(instance['ReadReplicaDBInstanceIdentifiers']),
                    aws_type='AWS::RDS::DBInstance',
                    resource_id=instance['DBInstanceIdentifier']
                )