Total 6 digit numbers possible with start digits as 123 are 123000 to 123999.
Hence, 1000 such numbers are there .
Now, the number should be exactly divisible by 5,7,9 . Take their LCM which is 315 .
Now, possible numbers which are divisible are =>
Floor (1000 / 315) = Floor ( 3.17) = 3
Hence, 3 numbers are possible between 123000 and 123999 which are divisible by 5,7 and 9.