Part 1
5b < 2b
5b-2b < 0
3b < 0
b < 0/3 ... see note below
b < 0
We determine that b is negative since it is less than zero.
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Part 2
7b > 3b
7b - 3b > 0
4b > 0
b > 0/4 .... see note below
b > 0
This time b is positive.
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Note: The inequality sign does not flip because we didn't divide both sides by a negative value.