Equation of trajectory of a particle projected from a point on ground is $\mathrm{y}=\left(\mathrm{x}-\frac{{\mathrm{x}}^2}{240}\right)$where x and y are in metre. If $\mathrm{g}=10\mathrm{m}/{\mathrm{s}}^2$, velocity of projection is

$\mathrm{y}=\mathrm{x}\left(1-\frac{\mathrm{x}}{240}\right)$

Comparing this equation with the standard equation 

$\mathrm{y}=\mathrm{xtan\alpha }\left(1-\frac{\mathrm{x}}{\mathrm{R}}\right), \mathrm{We}\mathrm{get}$

$\mathrm{tan\alpha }=1\Rightarrow \mathrm{\alpha }={45}^0$and Range = 240 m

$\mathrm{Now}\frac{{\mathrm{u}}^2}{\mathrm{g}}\sin 2\mathrm{\alpha }=240\Rightarrow \frac{{\mathrm{u}}^2}{10}\sin (2\times {45}^0)=240\Rightarrow \mathrm{u}=20\sqrt{6}\mathrm{m}/\mathrm{s}$