A box weighs 90 grams.
Write down, in terms of b, the weight of b boxes.

Let B = the weight of box B

Let 2B = the weight of box A

Let 2B + 30 = the weight of box C

B + 2B + 2B + 30 = 640

5B = 610

B = 122 pounds, weight of box B

2B = 2(122) = 244 pounds, weight of box A

2B + 30 = 2(122) + 30 = 274 pounds, weight of box C

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