Answer:
I would say 720
Step-by-step explanation:
one possibility that comes to my head is stack them on top of each other in many ways
-- Kenny's weight is 6/7 of Melvin's weight.
-- Melvin's weight is 7/7 of Melvin's weight.
-- The ratio of Kenny's weight to Melvin's weight is (6/7) / (7/7) = 6/7 .