Another word problem - how fast is the length of the shadow decreasing

Hi

Again I don't know what equation to use to solve this. Help please

Here is what we know:

- a spotlight on the ground shines on a wall 14 metres away

- a man 2 m tall walks from the spotlight toward the building at a spped of 1.8 m/s

Question: How fast is the length of his shadow on the building decreasing when he is 5 metres from the building?

I am leaving the computer for tonight but if you can lay out the steps of what I need to do to solve this I would appreciate it.

Thanks in advance