Easier to consider the function
f'(x)=0 at x=0 and x=-2
f(x) has its local extremes at x=0 and x=-2.
Hence, y has its local extremes at x=0 (minima) and x=-2 (maxima).
[Use 2nd derivative test to figure if it's a minima or maxima.
f''(0)=6>0 (indicates minima)
f''(-2)=-6<0 (indicates maxima)
The local extremes are y=0 (minima) and (maxima).