100 million years later ducks become the dominant species on earth, and they kill humans for food. one day the duck decide to have a little fun. They suspended humans on a vertical platform and dropped at a switch of an electrical signal, then fire weapons in mid air to kill human.

one party of ducks sat in a boat 138meters (horizontal distance) from the vertical platform on which the human were suspended. The guns, once fired, lanuched self-accelerating bullets with a constant horizontal acceleration of 7 meters per second squared. Guns were fired perfectly horizontally to hit the human targert as it passed the shoulder height of the duck.

Ducks find it not sporting to fire guns from a perched position in a boat. As such, they fire them only while flying. If a duck flies 100meters at 5meters per second(constant velocity) prior to "beaking" the trigger, and the electrial switch to drop the human is triggered at the exact same instant as "beaking", how high is the platform (measured from duck's shoulder height to top of platform)?

You can reglect the effect of gravity on the bullet.