Place commas according to the periods and then write the number names.
(b) 842907
842907 is written as 8,42,907
842907 can be written as Eight lakh forty-two thousand nine hundred seven.
Write the number according to Indian Place Value Chart. Insert commas to separate the periods:392689
Write the number according to Indian Place Value Chart. Insert commas to separate the periods: 56903275
(e) 1761829