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. So let's see, f prime, f prime of x is going to be 1.5 x to the negative 1.5, just using the power rule over here. So f prime of four, f prime of four is equal to 1.5 times four to the negative 1.5, which is of course equal to 1.5 times 1.5. Four to the 1.5 would be two, four to the negative 1.5 is going to be 1.5.