Tom was in control of the bike, so no appeal for him.
Dick's appeal rests on the definition of helmet/hat when the act was passed. Does a hard hat count as a helmet? Try the mischief rule, mention Heydon's case.
Harriet's case comes under ejusdem generis, because 'other such vehicle' when taken in context of 'bike, skateboard' means something like those two, and a hoverboard sounds similar to a skateboard. Ask Marty, he'll know about it, Doc Brown too.
Basically you want to run through all the rules of interpretation, so the 3 Latin rules, the Literal, Mischief, Purposive, and Golden Rules, and then the intrinsic and extrinsic aids. You'll have to find out whether these foreign findings can be used in the courts. Then solve the 3 problems.