Now suppose that the weight attached to the spring is pulled down a further 5cm from its equilibrium positions and released from rest. Show that newtons second law leads to the dynamic equation (in SI units)

Question

Now suppose that the weight attached to the spring is pulled down a further 5cm from its equilibrium positions and released from rest. Show that newtons second law leads to the dynamic equation (in SI units)
d^2z/dt^2 + 36z - g = 0 
where z(t) measures the extension of the spring from its natural lenght and g is the acceleration due to gravity.

The first part of this question was related to Hooke's Law which i have answered correctly, i am just unsure how you start this particular question.