One tract can be ploughed with 6 tractors for 4 days ifthey plough 120hectares a

One tract can be ploughed with 6 tractors for 4 days ifthey plough 120hectares a day. Two of the tractors were moved toanother tract. The rest 4 ploughed the same tract for 5 days. Howmany decares average a day ploughed the 4tractors?