Related Rates: Shadow Problem with Moving Object

[synergix]

Homework Statement

A spotlight on theground shines on a wall 12 m away. If a man 2m tall walks from the spotlight toward the building at a speed of 1.6m/s. how fast is the length of his shadow on the building decreasing when he is 4m from the building?

The Attempt at a Solution

x=4m dx/dt=1.6m/s dy/dt=?

I am kinda of stuck on this one. I know that as x decreases z and y will also decrease. But I am really not to sure how to proceed on this one any hints?

 

[Dick]

You need a relation between x, the distance from the wall and y, the height of the shadow. Draw a picture and find two similar triangles.