It's definitely possible. What you need to do is set up a NAT configuration using an extended ACL, a route map and a NAT pool on router B. The ACL will dictate what traffic will be subject to NAT and the NAT pool will define the translated source. You'll likely need a static route for the translated source on router C, pointing back to router B.
As rafael_acc has pointed out, this looks more like a homework assignment than a real-life problem, so I'm only providing general direction rather than a working configuration. Hopefully that sets you on the right track.
Check out the Cisco Learning Network for a more education-oriented forum as well. It's definitely worthwhile.
