Assume City Corp needs an insurance contract to cover $100m in risk. The primary insurance co writes the $100m policy and approaches 3 reinsurers to divide up the risk. Reinsurer Arsenal writes a policy for 20m xs 10m Reinsurer Bournemouth writes a policy for 30m xs 30m Reinsurer Chelsea needs to write a policy for how much to cover the remaining limit for the primary insurer?