Finding the derivative when given a graph

[jemadd2]

Okay so I was given a graph of a straight line that crosses the X-axis at -0.25 and the Y-axis at 1. It says:
The graph of the function f(x) is given above. Find f ' (1/2).
Im confused on what to do. Somebody told me its just finding the slope and you should draw a tangent line but I'm not sure how to do that.

 

[tkhunny]

Sorry, but you should not be in a Calculus class if you cannot find the slope of a line.

You have two points (-0.25,0) and (0,1). These two points define a line. Tell me again that you cannot find the slope of the line so defined.

Whoever told you to draw a line tangent to a line needs to rethink tutoring aspirations.