Complete step by step solution:
Value of books sold in first week\[ = Rs. 285891\]
Value of books sold in second week$ = Rs. 400768$
Total sale of books$ = $ Sale in first week$ + $ Sale in second week$
= Rs. 285891 + Rs. 400768
= Rs. 686659
Hence, the sale for two weeks together was $Rs. 686659$.
Since $Rs. 400768 gt; Rs. 285891$, sales in the second week were greater than the sales in the first week.
$ \Rightarrow Rs. 400768 - Rs. 285891 = Rs. 114877$
Hence, the sale in the second week was greater than the first week by $ Rs.114877 $.
For finding the net sale we have just combined the sales of two weeks i.e. we have simply added the two given values and in the second case to find out the greater one of the two, we have compared the two sales, and subtracted the two sales given to find out by how much the greater sale was compared to the smaller sale.