Area of floor of a hall is given by the expression $\left(a^2+9 a+20\right) m ^2$. If $a=2 m$, which of the following can be the dimensions of the hall?
While factorising the algebraic expression $20 x^2+5 x y^2-25 x y z$, a student followed the steps given below: In which step did he make his first mistake? Step I: $5 \times 2 \times 2 \times x \times x+5 \times x \times y \times y-5 \times 5 \times x \times y \times z$ Step II: $5 \times x(2 \times 2+y \times y+5 \times y \times z)$ Step III: $5 x\left(4+y^2+5 y z\right)$