20g + 12 = -12 + 18g
What you do to one side,
do the same to the other.
20g + 12 = –12 + 18g
subtract 12 20g + 12 – 12 = –12 + 18g – 12
leaves you 20g = –24 + 18g
now sub 18g 20g – 18g = –24 + 18g – 18g
leaves you 2g = –24
divide by 2 g = –12
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