Okay. Go on the TfL site, search travel cards and there will be a PDF breakdown of adult fares and destinations. You’ll find that an off-peak daily travel card for Zones 1-9 inc. Watford Jct. is £18.00. Cheaper if you get an Oyster card though.
A bit more info for you. If you purchase an Oyster Card and use it to travel from Victoria to Watford Junction the fare (single) will cost you £5.50. Specifically, the chosen route would be Victoria - Euston (tube Victoria line), Euston - Watford Junction (West Midlands Trains). If the timing is...
I’ve just checked the TfL site re.travel card areas and fares. You can purchase an off-peak daily travel card for £18.00 which permits travel in zones 1-9 + Watford Junction.
Yes you can. Presumably you are travelling from the south into London. Once you’re at any London station you can purchase an Oyster card or a daily travel card (TfL) which permits you to travel to Watford. Check out TfL (Transport for London) website for all info/fares/timetable.