What Train Tickets To Get

[Irishdancer]

I have to go to London on Saturday and then to ds who lives in Herne Bay. I wondered if any one can tell me on the train to Herne Bay what is the furthest you can get a train to Kent which is in zone 6 the train station I will be going to London from is a zone 6 my other dd is going to pick me up from the train so I am trying to find out how far I can go with just a travel card then get picked up.