A cloud architect is designing a new VPC with a 10.0.0.0/16 CIDR block for a three-tier application. The web tier subnet currently needs 200 usable IP addresses, but the architect wants to reserve enough room to triple the tier's capacity within the same subnet over the next two years without renumbering. The organization also mandates that subnet CIDR blocks be sized as small as possible while still meeting the projected need. Which CIDR block should the architect assign to the web tier subnet?