Calling BG_ABSENCE_DURATION from PL/SQL procdeure

Hi,

I am trying to call BG_ABSENCE_DURATION formula from PL/SQL procedure  as below:

declare

  days_or_hours                 varchar2(80);

  L_invalid_msg                 varchar2(250);

  date_start                    DATE;

  date_end                      DATE;

  time_start                    varchar2(80);

  time_end                      varchar2(80);

  L_asg_start_time                varchar2(80);

  L_asg_end_time                  varchar2(80);

  L_asg_pos_start_time            varchar2(80);

  L_asg_pos_end_time              varchar2(80);

  ABSENCE_ATTENDANCE_TYPE_ID    number;

  l_assignment_id       number;

  L_DATE_EARNED         DATE;

  L_BUSINESS_GROUP_ID   NUMBER;

  l_formula_id     number;

  l_effective_date date;

  l_inputs         ff_exec.inputs_t;

  l_outputs        ff_exec.outputs_t;

  l_loop_cnt       number;