Table COST relationship

Hi Gurus,

I'm new in queries world I'm building InfoSet for finance team where everything was going smooth to this point.

It is actually very simple one, just MAPL, PLPO, CRHD and CRCO.

But now I have to add also one information from COST table (field TKG008)  and I'm not able to find relation between COST and any of tables mentioned above.

Can you please suggest

Regards