C(b) = 2.75b + 10
This is based of the f(x) = mx + b formula, where m is the slope, x is the variable (or input) and b is the y intercept. In this circumstance the slope is 2.75, so we change m for 2.75. The variable is the amount of books so we change it for b (like it says in the word problem), and and 10 is the starting cost, so it’s the y intercept, so we change b for 10.
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