A spotlight is on the ground 20m away from a wall and a 2m tall person is walking towards the wall at a rate of 1.5m/s . How fast is the height of the shadow changing when the person is 8m from the wall? Is the shadow increasing or decreasing in height at this time?

i know i need to find dh/dt, which equals dx/dt * dh/x.

Is it possible to find dh/dx? (ie the relation between height of shadow and distance from wall)

Thanks in advance.