factor by grouping: (x^3 + x^2) -(16x +16)
you can take x^2 out of the first 2 and get x^2(x+1)
take 16 out of 2nd 2 and get 16(x+1)
looks like x^2(x+1) - 16(x+1)
if you think of it as "un-distributing" it becomes (x^2-16)(x+1)
x^2-16 then factors into (x+4)(x-4) so it all looks like (x+4)(x-4)(x+1)=0
set each factor equal to zero x+4=0, x-4=0, x+1=0 and solve
x=-4,4,-1