Answer: 
<u>Reorder the terms</u>
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Solving for variable 'a'.
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Move all terms containing a to the left, all other terms to the right.
<u>Add '15' to each side of the equation.</u>
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<u>Combine like terms: -15 + 15 = 0
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<u>Combine like terms: 6 + 15 = 21
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<u>Divide each side by '3'.
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