f(3) is the elevation of a mountain climber after 3 hours of climbing.
So we are given a line that relates time to elevation. We are also given that the equation of the line is f(x) = 125x + 50. From looking at the graph given, we can see that x is the time, in hours, and y, or f(x), is the height, in feet. We are asked to find f(3) and interpret it's meaning.
To find f(3), we would have to find what f(x) is when x = 3. To do this, lets plug in 3 for x into the given equation:
f(3) = 125(3) + 50 = 425
So f(3) = 425. Now, we already know that x is the time in hours and y, or f(x), is the elevation in feet. We set x to 3 when solving for f(3). We have also found that f(3), or y when x = 3, is 425. So f(3), or 425, is the elevation after 3 hours.
I hope you find my answer and explanation to be helpful. Happy studying.