Ah ok. so you have created a layer 3 VPN (which has different subnets at either end). If you go to computer B and change its IP to 10.10.21.x with a gateway of 10.10.21.240 you should be able to ping the LAN IP of router a (10.10.11.240).
If you want to extend 10.10.11.x subnet from router A to router B you need to configure a Layer 2 VPN tunnel.
