A hiker leaves camp at 6 A.M. to begin his descent from an elevation of 3,200 feet. He descends at the rate of 800 feet per hour. Suppose you are writing a function in slope intercept form, f(x) = mx + b, to represent this situation. Which choice is the value of b?
A) 4
B) 6
C) 800
D) 3,200