Each letter in the word is moved one step forward to obtain the corresponding letter of the code.

Justification:      

In the second and third statements, the common code is '9a' and the common word is 'not'.

So, '9a' means 'not'.
In the first and second statements, the common codes are '7c' and '3a' and the common words are 'is' and 'Eternal'.
So, in the second statement, '8b' means 'enmity'.

 Each letter in the word is moved one step backward to obtain the corresponding letter of the code

- There are 7 letters in the word

- The middle letter has been left intact

- The first and the last letters  of the word have interchanged their position. Similarly, the second and the third letters and the fifth and sixth letters have interchanged their position.

  1 2 3 4 5 6 P R O B L E 7 M ? 7 1 6 2 5 3 M P E R L O 4 B

Similarly,  1 2 3 4 5 6 N U M B E R 7 S ? 7 1 6 2 5 3 S N R U E M 4 B

The alphabets are soded as shown :

$$\begin{gathered} E ? N ? T ? R ? Y ? S ? A ? D \\ 1 2 3 4 5 9 7 8 \end{gathered}$$

N is coded as 2,

E as 1,
A as 7,
T as 3   and
S as 9.
So, NEATNESS is coded as 21732199.

Justification:      

In the first and third statements, the common word is 'na' and the common word is 'are'.

So, 'na' means 'are'.
In the second and third statements, the common code word is 'tok' and the common word is 'bad'.
So, 'tok' means 'bad'.
Thus, in the third statements, 'tim' stands for 'they'.

In the first and second statements, the common code digit is '2' and the common word is 'carpet'.

So, '2' means 'carpet'.

In the second and third statements, the common code digit is '6' and the common word is 'one'.

So, '6' means 'one'.
Therefore, in the second statement, '5' means 'dust'.

Here E = 5 = 5/1 = 5

=> READ = 18 + 5 + 1 + 4 = 28/4 = 7

=> DEAR = 4 + 5 + 1 + 18 = 28/4 = 7