Write the degree of the following polynomials

$11-2 y^{2}$

On dividing $x^{3}+a x^{2}+19 x+20$ by $(x+3),$ if the remainder is $a,$ then find the value of $a$.

Factorise the following:

$25 x^{2}+16 y^{2}+4 z^{2}-40 x y+16 y z-20 x z$

Classify the following as a constant, linear,quadratic and cubic polynomials:

$3 x^{3}$

Show that :

$2 x-3$ is a factor of $x+2 x^{3}-9 x^{2}+12$