Answer
a. In Newton’s second law, solve for the acceleration.
The net force is the gravitational force.
$$ a = \frac{F}{m_{object}} = \frac{1}{m_{object}} G \frac{m_{object}M_{planet}}{d^{2}} = G \frac{M_{planet}}{d^{2}}$$
b. The mass of the object cancels out. The gravitational acceleration of an object does not depend on its own mass, but only on the mass M of the planet and its radius.
