Have linksys wirless N router near modem and want to extend signal to guest house 20 meters away. Tried extenders, but did not

Linksys routers should be good for about 100 feet. In your set-up make sure that there are no obstacles between the router and the guest house. Try re-positioning your router.

(My Linksys N Router has a good signal 40 feet away, over 2 floors, and through 4 walls).