Code:
declare 
	v_purchase number; 
begin
     	SELECT min(software.purchase_cost)
   		into v_purchase
      from hardware, software
      where :hardware.hw_serial_num = software.hw_serial_num;
      
      go_block('software');
      first_record;
     
      for i in 1..:system.last_record 
       loop
       	   go_record(i);
       if nvl(:software.purchase_cost,0)
...