This is a great problem because it illustrates the gravitational principe that all things on Earth fall at the same rate of gravitational acceleration which is around 9.86m/s^2.
Given the above fact, and maybe contrary to your intuition, if we neglect air resistance, we do not even need to know the mass of the whatever object is falling. We take this fact for granted but it shouldnt be forgotten that on of the smartest men in ancient Greece (Aristotle) thought that heavier masses fall more quickly to earth than lighter masses.
All we need to know to solve this problem is is the rate of gravitational acceleration and our kinematic formulas for one-dimensional motion with constant acceleration (which we assume there is constant acceleration because to a high degree of approximation, the gravitaitonal acceleration on earth's surface is nearly constant).
This understanding leads to the following equations:
y(t) = y0 + v0t + 1/2 g t^2
v(t) = v0 + g * t
because v0 is zero because the object starts from rest, the first and second equation become:
y(t) = y0 + 1/2 g t^2
v(t) = g * t
Thus we have a system of two equations, with two unknowns: t and y0, where t is the time it takes for the object to hit the ground and y0 is the object's initial height.
I hope this helps!!
