Find the greatest common factor of the given monomials.

$9x{y}^2$, $-6xy$, $-3x$

The greatest common factor of the given monomials$14x^3{y}^3$, $21x^5{y}^2$, $35x^6{y}^6$ is $k{x}^3{y}^2$.  Find the value of $k$.

If the greatest common factor of $p^2{q}^8{r}^3,$ $-p^6{q}^7{r}^3, \text{and}$ $p{q}^5{r}^2$ is of the form $p^x{q}^y{r}^z$, then write the value of $x+y+z$.

Find the greatest common factor of the given monomials.

$24a^{2}b$, $-16abc$, $32a^2{b}^2{c}^3$, $36a{b}^2{c}^2$

Factorise the expression: $a^2-ax$

On factorising the expression $3a^2-9$ we get $3(a^2-k)$, find the value of $k$

Factorise the following expressions.

$5ax-5a^2{x}^2$

If $\mathrm{\pi }{R}^2-\mathrm{\pi }{r}^2=\mathrm{\pi }\left(R+r\right)\left(R-k\right)$, then find $k$.

Factorise the following expressions.

$3a{b}^2-6a^{2}b$