Barbara buys a box of pens for $4. For every additional box she buys, she gets a $1 discount. Which expression represents the total cost of the pens, c, as a function of the number of boxes, b? A. c=f (b) = 4b-1 B. c=f (b) = 4b+1 C. c=f (b) = 3b+4 D.
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