To serve Web traffic for a popular product your chief financial officer and IT director have purchased 10 m1. large heavy utilization Reserved Instances (RIs), ...

To serve Web traffic for a popular product your chief financial officer and IT director have purchased 10 m1.
large heavy utilization Reserved Instances (RIs), evenly spread across two availability zones; Route 53 is used to deliver the traffic to an Elastic Load Balancer (ELB). After several months, the product grows even more popular and you need additional capacity. As a result, your company purchases two C3.2xlarge medium utilization Ris. You register the two c3.2xlarge instances with your ELB and quickly find that the m1.
large instances are at 100% of capacity and the c3.2xlarge instances have significant capacity that's unused.
Which option is the most cost effective and uses EC2 capacity most effectively?