(a) At equilibrium position, the net force is zero. Therefore, the spring force must be equal and opposite to the weight of the block.

The equation for the net force on the block is as follows,

The expression for the spring force is,

Here, k is the spring constant and x is the displacement of the block from the equilibrium position.

Replace with, with and rearrange the expression for k.

Here, m is the mass attached to the spring and g is the acceleration due to gravity

Substitute for m, 9.81 m/s2 for g and 36 cm for x.

Thus, the spring constant is approximately