It tells us what the corresponding f of x is. And they say what is the best estimate for f prime of four? So this is the derivative of our function f when x is equal to four. Or another way to think about it, what is the slope of the tangent line when x is equal to four for f of x? So what is the best estimate for f prime of four we can make based on this table? So let's just visualize what's going on before we even look at the choices. So let me draw some axes here.