Answer:
The speed of the package of mass m right before the collision 
Their common speed after the collision 
Height achieved by the package of mass m when it rebounds 
Explanation:
Have a look to the diagrams attached below.
a.To find the speed of the package of mass m right before collision we have to use law of conservation of energy.
 
 
where  is Kinetic energy and
 is Kinetic energy and  is Potential energy.
 is Potential energy.
 and
 and  
 
Considering the fact   we will plug out he values of the given terms.
 we will plug out he values of the given terms.
So 
Keypoints:
- Sum of energies and momentum are conserved in all collisions.
- Sum of KE and PE is also known as Mechanical energy.
- Only KE is conserved for elastic collision.
- for elastic collison we have  that is co-efficient of restitution. that is co-efficient of restitution.
<u>KE = Kinetic Energy and PE = Potential Energy</u>
b.Now when the package stick together there momentum is conserved.
Using law of conservation of momentum.
 where
 where  .
.
Plugging the values we have 

Cancelling m from both sides and dividing 3 on both sides.

Law of conservation of energy will be followed over here.
c.Now the collision is perfectly elastic 
We have to find the value of  for m mass.
 for m mass.
As here  we can use that if both are moving in right ward with
 we can use that if both are moving in right ward with  then there is a
 then there is a   velocity when they have to move leftward.
 velocity when they have to move leftward.
The best option is to use the formulas given in third slide to calculate final velocity of object  .
.
So

Now using law of conservation of energy.
 
 



The linear momentum is conserved before and after this perfectly elastic collision.
So for part a we have the speed  for part b we have their common speed
 for part b we have their common speed  and for part c we have the rebound height
 and for part c we have the rebound height  .
.