Factorise: $6x^{n}4+5\times n_{3-10x+4}$

$Q2$ Factorise : a) $\right)$ $63x^{2}-112y^{2}b\right)$ $x^{2}$ $-10x+21$

$Q=E$ $Q2$ $I.$ Factorise: $28-31x-5x^{2}$ $2.$ Factorise: $3xy^{2}+9x^{2}y^{2}-6x^{2}y$ $\right)$ Factorise: $5x^{2}+25x+50$ $4$ .Factorise: $\left(x+5\right)^{2}-4\left(x+5\right)$ $l$ Evaluate: $\left(\left(9.1\right)^{2}-\left(4.2\right)^{2}\right)$ Factorise: $x^{2}+6ax+9a^{2}$ Factorise: $9a^{2}-b^{2}+4b-4$