Help with a Related Rates Problem! (tip of shadow)

[jessi88]

A light is at the top of a 16 m pole in a quarry. A truck 5m tall moves away from the pole at a rate of 4m/s. At what rate is the tip of the shadow moving when it is 18 m from the pole? At what rate is the length of its shadow increasing??

 

[tkhunny]

That's a lovely problem. Have you drawn a picture? Have you noticed the similar triangles? What work have you done?