Solve the given parts of following problem given below:

Problem: Assume the Earth's orbit around the sun is a circle and has radius 1.50 x 10⁸ km. This is a rough approximation of the Earth's true elliptical orbit.

Part A: What is the magnitude of the orbital velocity of the Earth in m/s?

Part B: What is the radial acceleration of the earth toward the sun, in m/s2?

Part C: Repeat parts a) and b) for the planet Mercury (orbital radius 5.79 x 10⁷ km; orbital period 88.0 days).

Please provide clear step by step solution with notes on concepts and equations being used in above problem.