Answer :
1/7 gallon = 1 batch
[multiply by 7 through]
1 gallon = 7 batches
[multiply by 8/9 through]
8/9 gallon = 7 x 8/9
8/9 gallon = 6 2/9
[Good enough to make 6 batches, not enough to make 7 batches]
So he can make 6 batches of collard green
[multiply by 7 through]
1 gallon = 7 batches
[multiply by 8/9 through]
8/9 gallon = 7 x 8/9
8/9 gallon = 6 2/9
[Good enough to make 6 batches, not enough to make 7 batches]
So he can make 6 batches of collard green