Plotting second order ode response

I have been trying to plot the curve of 'y', the step response of a differential equation but my code doesn't seem to work, please help.

clear all, close all, clc
y = dsolve('D2y+12*Dy+36*y=36', 'y(0) = 0','Dy(0) = 0')
pretty(y)

Answer 1

[Paul]

f=matlabFunction(y);
t=0:.001:1;
plot(t,f(t)),grid

If you have the Control System Toolbox:

step(tf(36,[1 12 36]))