You are hiking on a trail that leads down from the top of a mountain. at 1 p. m. you are at an elevation of 6000 feet. at 5 p. m. you are at an elevation of 4800 feet. what is your mean hourly change in elevation?

Okay to start this out. You started hiking at 1 P.M. You are at an elevation of 6000 ft. At 5 PM You are at an elevation of 4800 feet. 6000 feet - 4800 feet = 1200 feet in 4 hours.
Make a ratio 4(Hr):1200 Ft
                       3(Hr):900 Ft
                       2(Hr):600 Ft
                       1(Hr):300 Ft
So at the end of the equation your hourly change is -300 ft, because the elevation is going down.