Factorize the following.

$x^4+4$.

Factorise the following:

$x{y}^9-y{x}^9$

Factorise: $x^2+12x-45$

Factorise: $x^2-22x+120$

Factorise: $x^2-30x+216$

Factorise: $6-x-x^2$

Factorize the following algebraic expression by splitting the middle term:

$x^2-21x+108$

Factorise: $x^2+5x-36$