Need help on (A), THANKS.

(9 points) Suppose that f(x) = x4 7x3. (A) Find all critical values off. If there are no critical values, enter -1000. If there are more than one, enter them separated by commas. Critical value(s) = 0,21/4,-64827; (B) Use interval notation to indicate wheref(x) is increasing. Note: When using interval notation in WeBWorK, you use I for 00, -I for 00, and U for the union symbol. If there are no values that satisfy the required condition, then enter "{}" without the quotation marks. Increasing: (2 1/4, I) (C) Use interval notation to indicate wheref(x) is decreasing. Decreasing: (|,21/4) (D) Find the x-coordinates of all local maxima off. If there are no local maxima, enter -1000. If there are more than one, enter them separated by commas. Local maxima at x = -1000 (E) Find the x-coordinates of all local minima off. If there are no local minima, enter -1000. If there are more than one, enter them separated by commas. Local minima at x = 1000