This was a difficult manipulation of numbers, and I received 4 answers from Mahi Saraf, Anand Singhi, Pratik Poddar and Prakhar Prakash. Only two of these I found to be completely correct – from Mahi Saraf and Anad Singhi. That said, I found the approach from all of them to be very good and similar. Well done Mahi and Anand!
Here is the answer from Mahi, and I am also reproducing the answer from the original source.
6 + 66 + 666 …….
6 (1+11+111+1111…)
6(10-1/9 +100-1/9 + 1000-1/9 …..)
6/9 (10+100+1000……-100)
2/3(1(100 times) – 100)
2/3(1(98 times) followed by 010)
2({1(98 times) followed by 010} / 3)
2(037(32 times) followed by 03670)
074(32 times) followed by 07340
Hope you all enjoyed the puzzle!
Alok Goyal's Puzzles Page 
I think I emailed a solution too? 🙂