So this is going to happen when x is equal to zero. That I could, let me not skip steps. So this is going to happen when x to the third is equal to zero, or four minus five x is equal to zero. For x to the third equaling zero, well that's only gonna happen when x is equal to zero. And four minus five x equaling zero, we'll add five x to both sides. You get four is equal to five x. Divide both sides by five, you get four fifths is equal to x. So here, these are the two places where our derivative is equal to zero.