Try this one
`recordno`, `year`, `sem`, `stuid`,`subid`, `type`, ((100 / `working`) * `present` ) AS Percentage
((100 / `working`) * `present` ) < 75
`month` = @SelectedMonth
`subid` = @SelectedSubjectID;
This assumes that working is the total working days in the month, and that by inference, you calculate the percentage 100 divided by the total days, times the number of days attended (present).
Hope this helps