options and exercising

guys - I've had a quick search but can't find.

I've got a handful of THXO and ROYO that I want to exercise. I know I need to contact the Registrar - so does this mean I need to ask via Computershare for an "Exercise of Options" form for both THX and ROY? Or do I need to directly contact THX and ROY?

I'm assuming they send out a blank exercise form and I specify how many options I want to exercise and the amount I'm paying.

Does the registrar advise of the exercise price or is it my responsibility to do the maths and pay up the correct amount.

Exercising Virgin... :)