If You Throw a Stone into the Air at an Angle

Essay

If you throw a stone into the air at an angle of $\theta$ to the horizontal, it moves along the curve $y=x \tan \theta-\frac{x^{2}}{160}\left(1+\tan ^{2} \theta\right)$ ,
where y is the height of the stone above the ground, x is the horizontal distance.Suppose the stone is to be thrown over a wall at a fixed horizontal distance l away from you.If you can vary $\theta$ , what is the highest wall that the stone can go over? (Your answer will contain l.)