So it's going to be two plus the derivative, so the slope of this line, plus f prime of four times x minus four. So 4.36 minus four is going to be times 0.36. And that makes sense, you're starting at two, and you're saying okay, my change in x, my change in x is 4.36, so my change in y is going to be my slope times that change in x to get me that value, to get me that value right over there. So let's figure out, let's figure out what this, let's figure out what this thing, what this thing actually is. So to do that we need to figure out f prime of four. So let's go back up here. I'll try to leave, actually, I'll leave this little visualization here.