South Africa. (Bechuanaland - Bolivia). 1951. Air Mail envelope written from Bolivia addressed to Bechuanaland bearing Bolivia Air Mail Yvert 85, 90c lilac and orange and Yvert 86, 2b blue and orange tied by Cocharanba double ring '21st Feb 1951' , underpaid with m/s '2 1/2' in red crayon and bearing Bechuanaland postage due SG D4, 1/2d sage-green and SG D6, 2d violet applied and tied by Ramoutsa Sta. receiver '5th March' . Amazing combination for the Exhibitor of postage dues. Stamps Cat GBP 130 time 60 = 7800!