Ashley starts with 45 comics.
So in the first box:
x = 0, y = 45
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Each month, she adds 5 comic books to her collection
x (+1), y (+5) (for each month).
First month.
x = 0
y = 45
Second month
x = 1
y = 45 (+5) = 50
Third month
x = 2
y = 50 (+5) = 55
etc.
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B) is your best choice, as for every month add (+1), the comic books increase by 5 respectively.
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hope this helps