Just bored as shit, answer this question and get 20KLG.

If 8 grapefuit, 7 oranges & 3 lemons weigh the same as 3 oranges, 6 grapefruit & 6 lemons, if a grapefruit weighs 2/3 as much as a lemon & if a dozen oranges weighs 3 kilos, How much does a lemon weigh?