Answer:
The value is 
Explanation:
From the question we are told that
The speed of in a vacuum is 
The speed of light in the material is 
Generally the reflection of the material is mathematically represented as

=> 
=> 
Answer:
<h2>The answer is 9 kg</h2>
Explanation:
The mass of an object can be found by using the formula

f is the force
a is the acceleration
From the question we have

We have the final answer as
<h3>9 kg</h3>
Hope this helps you
May you please provide a picture of the table, so that I can see his error? Otherwise I can not solve.