(2/3 + 3/4 + 4/5) + (1/6 + 2/7 + 3/8) + ( 5/8 + 5/7 + 5/6) + ( 1/5 + 1/4 + 1/3) =
(40/60 + 45/60 + 48/60) + (56/336 + 96/336 + 126/336) + (210/336 + 240/336 + 280/336) + (12/60 + 15/60 + 20/60) = 133/60 + 278/336 + 730/336 + 47/60 = 133/60 + 47/60 + 278/336 + 730/336 = 180/60 + 1008/336 = 3 + 3 = 6