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