Answer:
b=-1
Step-by-step explanation:
you need to make sure that you can add 7 and have the answer be 4cm because, and if you subtract 4 from 7 you get 3 so the should add onto a -3 and the only way to turn the 3 into -3 is to multiply the 3 by -1
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the answer is 500. hope this helps give me brainlest please.
