If $x+3$ is a factor of $x^{3}+12 x^{2}+a x+60$ then $a=\ldots \ldots \ldots$

What should be subtracted from $p(x)=x^{2}+9 x+20,$ so that the resulting polynomial is divisible by $x+2 ?$

Determine the degree of each of the following polynomials:

$x^{3}-9 x+3 x^{5}$

Evaluate

$(153)^{2}$

The following expressions are polynomials? Justify your answer:

$\sqrt{3} x^{2}-2 x$

Factorise

$x^{2}+4 y^{2}+25 z^{2}+4 x y-20 y z-10 z x$