Answer : m = 60 kg
Explanation :
It is given that,
Net force acting on an object is, F = 12 N.
Acceleration produced on it,

Newton's second law of motion gives the measure of force acting on the object. i.e.
F = m a
m is the mass
Using second law of motion we get :



So, the correct option is (d).
Hence, this is the required solution.