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Best Answer

b + 9 = 21

Take the + 9 across the other side of the equals sign. a plus becomes a minus.

b = 21 - 9

so...

b = 12.

This can be checked by setting b to 12 in the first equation

b + 9 = 21

12 + 9 = 21

which is correct.

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14y ago
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Q: How do you work out b plus 9 equals 21?
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