Unit 1: Positive externalities associated with hydrogen bikes

This BBC clip shows the new hydrogen bike developed by Loughborough University

http://news.bbc.co.uk/1/hi/england/7655831.stm

a) What would be the private cost of owning a hydrogen bike?
b) What would be the private benefit of owning a hydrogen bike?
c) What would be the positive externalities/external benefits of the hydrogen bike?
d) Are there any negative externalities/external costs associated with the bike?