Let the number of books bought be x. Then,
Cost of x books = Rs. 80
         Cost of one book = Rs. 
If the number of books bought is x + 4, then
Cost of one book  = Rs. 
According to given condition,

∴                  

            



                          
                       
             

     

                                
or                                   
                                  
[∵ x cannot be negative]
Hence, the number of books is 16.

Suppose the time taken by the faster pipe is x minutes.
∴ Time taken by the slower pipe = (x + 3) minutes
Now,
Portion of cistern filled by the faster pipe  and portion of cistern filled by the slower pipe =  and portion of the cistern filled by the both in 1 minute

    
It is given that,
Portion of the cistern filled by both 1 minute         ...(ii)
Comparing (i) and (ii), we get
                        

                         
                  
                       
                

(which is rejected)  Hence, time taken by the faster pipe = x = 5 minutes and time taken by the slower pipe = (x + 3) = 5 + 3 = 8 minutes.

Let the width of the gravel = x metres. Then,
Each side of the square flower bed
= (44 – 2x) metres.
Now, Area of the square field
= 44 x 44 = 1936 m²
and Area of the flower bed
= (44 – 2x)² m²
∴ Area of the gravel path
= Area of the field – Area of the flower bed
= 1936 – (44 – 2x)²
= 1936 – (1936 – 176x +4x²)
= (176x – 4x²) m²

Cost of laying the flower bed
= (Area of the flower bed) (Rate per sq. m)

Cost of gravelling the path
= (Area of the path) x (Rate per sq. m)
= 
It is given that the total cost of laying the flower bed and gravelling the path is Rs. 4904.
∴ 11 (22 – x)² + 6 (44x – x²) = 4904
⇒ 11(484 – 44x + x)² + (264x – 6x²) = 4904
⇒ 5x² – 220x + 5324 = 4908
5x² – 220x + 420 = 0
⇒ x² – 44x + 84 = 0
⇒ x² – 42x – 2x + 84 = 0
⇒ x (x – 42) – 2 (x – 42) = 0
⇒ (x – 2) (x – 42) = 0
⇒ x = 2 or x = 42
But, x ≠ 42, as the side of the square is 44 m.
Therefore, x = 2.
Hence, the width of the gravel path is 2 metres.