please help with this calculus problem thanks

5. Amusement Engineers working for the amusement park Dampworld must build a water slide that is 20 ft tall. They must ensure that the slope is -3 at some point along the slide, which is perfect for taking pictures and then selling them to the riders). What should the horizontal width of the slide be to guarantee that there is such point? 5. Amusement Engineers working for the amusement park Dampworld must build a water slide that is 20 ft tall. They must ensure that the slope is -3 at some point along the slide, which is perfect for taking pictures and then selling them to the riders). What should the horizontal width of the slide be to guarantee that there is such point