I'm going to neglect air resistance here, and assume that
the projectiles are moving as if they're in vacuum.
The only force on the projectiles is the force of gravity.
Gravity only affects the vertical speed of the projectile.
There's NO horizontal force on the projectile, so there's
nothing to make it speed up or slow down. It keeps the
same horizontal speed for as long as it doesn't crash
into the ground or hit something.
Distance = (speed) x (time)
Projectile-A flew horizontally at 40 m/s for 6 seconds.
It covered (40 m/s) x (6 sec) = 240 m .
Projectile-B flew horizontally at 60 m/s for 4 seconds.
It covered (60 m/s) x (4 sec) = 240 m .
Projectile-C flew horizontally at 50 m/s for 5 seconds.
It covered (50 m/s) x (5 sec) = 250 m .
Projectile-D flew horizontally at 80 m/s for 4 seconds.
It covered (80 m/s) x (4 sec) = 320 m .
I'll stop there, and leave it to you to calculate which one covered
the greatest horizontal distance. I'm pretty sure you can do it.
