Answer:
Gregory gets 4 coffee for free and the total number of coffee he gets is 16.
Explanation:
Given that when customers pay for 3 coffees, they get another coffee free.
So, for the cost of 3 coffee, 1 coffee is free.
Therefore, for the cost of 3n coffee, n coffee is free.
As Gregory pays for 12=3x4 coffees, the number of free coffee, n=4.
So, the total number of coffee Gregory = 12+4=16.
Hence, Gregory gets 4 coffee for free and the total number of coffee he gets is 16.