One-half of the employees of a company earns over Tk.18000 per month. One-third of the remainder earns between Tk 15000 to Tk.18000. What part of the staff earns below Tk.15000?

প্রশ্নঃ One-half of the employees of a company earns over Tk.18000 per month. One-third of the remainder earns between Tk 15000 to Tk.18000. What part of the staff earns below Tk.15000?