Answer :
[tex]3x^2+12x-36=3(x^2+4x-12)=3(x^2+6x-2x-12)\\\\=3[x(x+6)-2(x+6)]=3(x+6)(x-2)[/tex]
[tex]3x^2 +12x-36=3(x^2+4x-12)=3(x^2-2x+6x-12)=\\\\=3[x(x-2)+6(x-2)]=3(x-2)(x+6)[/tex]