(c) For number between 600 to 700 :
Number of 6 at the units place = 10
Number of 6 at the tens place = 10
Number of 6 at the hundredth place = 100
For number between 501 to 599 :
Number of 6 at the units place = 10
Number of 6 at the tens place = 10
Hence, total number of 6 between (501 – 700)
= 10 + 10 + 100 + 10 + 10 = 140