(b) the centripetal force on a planet is provided by the gravitational force between it and the Sun
Remember the circular motion stuff. You will need it all again here. There is not much else to say about this statement really.
(c) the equation
Learners will also be expected to derive this equation from first principles.
This looks tricky but in fact if you equate the centripetal force equation with that for gravitational force and force, cancel some stuff and substitute in for the velocity using the period and it will all be OK.