y=x3+6x2+9x-11,
y'=3x2+12x+9=0 at stationary points⇒x2+4x+3=0=(x+3)(x+1), so x=-1 and -3.
y=-1+6-9-11=-15; and -27+54-27-11=-11.
Stationary points at (-1,-15) and (-3,-11).
y"=6x+12 is positive at x=-1, and negative at x=-3 so (-1,-15) is a minimum (concave up) and maximum (concave down) at (-3.-11).