Sorry to take so long.
ok … you know the actual formula, so you don't need the quadratic equation … that saves time!
If your calculation of the spring constant is correct (and you haven't shown us, so I can't check it), then you must
use the mass of man+car, because that's what the suspension is having to put up with!
"sketch graph" means that you don't need to put in any values … the examiner only wants to see the rough shape
of the graph (eg, is it a line, a parabola, a sine curve, a V-shape, …).
So just say in words what the shape is … and then draw it!
To start you off … in words, what happens to the height of the car if there is no
suspension (ie suspension not functioning)?