$a)w_1\cdot w_2=\left(-3x^2+2x-1\right)\cdot \left(-2x-4\right)=6x^3+12x^2-4x^2-8x+2x+4=6x^3+8x^2-6x+4$  

$b)w_2^2-w_1={\left(-2x-4\right)}^2-\left(-3x^2+2x-1\right)={\left(-2\left(x+2\right)\right)}^2+3x^2-2x+1=4\left(x^2+4x+4\right)+3x^2-2x+1=4x^2+16x+16+3x^2-2x+1=7x^2+14x+17$