To know the sales of the 2 weeks together, add the result of the two
16,369 + 352,258 = 368,627 rupees
Reply in the two weeks together he sold 368,627 rupees
now we subtract the fourth week with the third to know how much the sale increased
352,258 - 16,369 = 335,889 rupees
in the fourth week it sold more books than the third by Rs 335,889 more than the third.