Question 147588
The number of radio stations at any year is

f(x) = 214.3x-415,368

in 1980, x=1980

so f(1980) = 214.3(1980)-415,368   =  8964

slope of the graph is the change in f(x) due to a unit change in x (like the slope of the line y= m*x+c is m)

so the slope is 214.3

To interpret as a rate, look at what the function f(x) represents: the number of radio stations in a year.

The rate represented by the slope is 214.3 radiostations per year.

Hope this helps,

Adam