# How to setup Related Rates problem?

A flood light is on the ground 45 meters from a building.  A thief 2 meters tall runs from the floodlight directly towards the building at 6 m/sec.  How rapidly is the length of this shadow on the building changing when he is 15 meters from the building ?

This is problem from first calculus course taught in a University.  This is a related rates problem.

Please help setup this problem.  Is this going to be a triangle?  15 meters from building might be one side of the triangle.  Change of length of shadow on building might be another side of triangle.  What would be the hypotenuse?

Is flood light projected at an angle on the bulding?
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Commented:
It says the floodlight is on the ground, so I would have the feet of the thief and the base of the wall also on the ground. Project from the lamp through the 2m height to the wall and calculate the height of the shadow. This is based on the changing distance of the 2m height from the lamp.  He runs at a constant speed so you need to find the change in height of the shadow at the 15m point. The shadow is getting shorter.

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