HI Hassan,
RP_CALC_DATE_IN_INTERNAL this is the function module u pass ur input start date and u can subtract the 360 days u will get the new date some xxxx
by using this u can write u r select query like
select (no of joiner ) from xxxx (custom table )
where joining date GE this newly coming date
and joining date LE (ur input date ).
but here u should have the employee joining details by date range
Regards ,
Pramodh