Can someone help with #2 a and b? Thanks!

2. Shadow problem (in which similar triangles may be relevant). A spotlight is on the ground 50 feet from a residence hall with vertical sides. Chris, who is 6 feet tall, starts at the spotlight and walks directly toward the hall at a rate of 4 feet per second. (a) First draw a picture of the situation. Then determine how fast the top of Chris's shadow is moving down the residence hall when Chris is 20 feet away from the hall. (Note: Remember that when you draw a picture, the distance between the spotlight and the resi- dence hall is fixed. Define the variables relevant to the problem, then state what you wish to find and what you know, and finally solve the problem.) (b) Is the rate of change of the shadow increasing, or is it decreasing, as Chris approaches the residence hall? Explain why, in a complete sentence