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carrie's catering is having a special on their box lunches. the minimum purchase is 14 boxes for $126. each additional box is $7. if x represents the number of boxes over the minimum, which of the following equations represents the cost of box lunches during this special?
a. y = 7x + 126
b. y = 126x + 7
c. y = 126x - 7
d. y = 126 - 7x