[flaubere]

Not sure why you are asking this in this thread, but the implication is that the bullets are fired from ground level, not necessarily horizontally. The maximum distance a projectile can travel when fired from ground level is the basic first result of ballistics.

[tyleo]

I think I understand. From height 0 figure out what gun angle gives the largest distance and then calculate the area of the circle with that distance as radius.

[xNeil]

In the JEE, you generally assume the range to be the distance the projectile covers before reaching the launch height again, unless specified otherwise.