im really stuck on this question could some one plz help me solve it.

An observer sees a ship from the top of a cliff of height 100 m. The ship is seen

through an instrument which measured the angle of depression to be 80°. The observer

then moved back a distance of 10 m, at which point the ship and the top of the cliff

were in line. Find the distance from the base of the cliff to the ship.

thanx

xxx