The length of a rectangular hall is 5 m more than its breadth.

(d) 30 m

Let the length of the rectangle be x m.

$\therefore$ Breadth of the rectangle $=(x-5) \mathrm{m}$

Area $=x(x-5)=x^{2}-5 x$

$\Rightarrow x^{2}-5 x=750$

$\Rightarrow x^{2}-5 x-750=0$

$\Rightarrow x^{2}-30 x+25 x-750=0$

$\Rightarrow x(x-30)+25(x-30)=0$

$\Rightarrow(x+25)(x-30)=0$

$\Rightarrow x+25=0$ and $x-30=0$

$\Rightarrow x=-25$ and $x=30$

Length cannot be negative.
∴ Length = x = 30 m