Related Rates Question. Help!

1. Oct 14, 2006

jen333

Hey, I have this one practise calculus question that I just can't seem to get. Any help would be greatly appreciated:

A light is on the ground 40ft from a building. A man 6ft tall walks from the light towards the building at 6ft/s. How rapidly is his shadow on the building becoming shorter when he is 20ft from the building?
(btw, the answer should be -3.6ft/s)

I've already drawn a diagram, but I'm not sure if triangle ratios would do any good.

2. Oct 14, 2006

StatusX

Were you able to find the height of his shadow as a function of his distance from the building?

3. Oct 14, 2006

Hint: $$\frac{6}{x} = \frac{y}{?}$$