So the width can be written as W=3L-6. (L is length and W is width). The maximum the width could be is 45mm, so try to use 45mm in place of W. 45=3L-6. Add 6 to both sides and you get 51=3L. Divide both sides by 3 and you get 17=L, where L is the length.
This is a question of combination. In other words, the question requires determination of number of ways in which 12 appetizers can be chosen form a total of 17 appetizers.
Therefore,
Possible number of 12 groups = 17C12 = 17!/[12!*(17-12)!] = 6188
It -2,-1 I hope this help
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