take no of days from 2 calender and display oracle query data in gridview

hi
guys 
i have 2 calender i.e 1> between date...................2> to date....Go button
i have to select date from these 2 calender like....frm this date to this date.(no of days)....then click Go button..
i have this oracle query
"select FT.FILE_DEPARTMENT,u1.user_designation,U1.USER_NAME,(count(u1.user_designation)/30)*24 as avg_file_disposal_in_hours from filetrans FT,USERS U1 where U1.USER_NAME LIKE '%Secretary/Pr. Secretary/Addl. CS%' AND FT.OFFICE_CODE=U1.OFFICE_CODE AND FT.DESPATCH_DATE_TIME between sysdate-30 and sysdate and FT.RECEIPT_DATE_TIME between sysdate-30 and sysdate group by FT.FILE_DEPARTMENT, u1.user_designation, U1.USER_NAME"
this query displaying data from 
sysdate-30 and sysdate my work is provide such option so that user can select date from these two calender and based ...