Answer:

Explanation:
There is no external force applied, therefore there is a moment's preservation throughout the trajectory.
<em>Initial momentum = Final momentum. </em>
The total mass is equal to

Where,
mass of ship
mass of fuell expeled.
As the moment is conserved we have,

Where,
Velocity of fuel
Velocity of Space Ship
Solving and re-arrange to
we have,



Where c is the speed of light.
Therefore the ship be moving with speed


I believe your answer is correct, because 8.7*10^-7 is equal to 0.00000085347.
Hope you do well!
When the ball reaches its original position, it will have the same speed (but would be traveling in the opposite direction). So the average speed is

regardless of how long the ball was in the air.
Well it breaks it away from rain or earthqukes depends but then depostion takes the rocks away and a delta takes it into the ocean