First, turn both expressions into an equation
6a-4=2a+56
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Now solve
Subtract 2a from each side
6a-4-2a=2a+56-2a
4a-4=56
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Add 4 to each side
4a-4+4=56+4
4a=60
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Divide each side by 4
4a ÷ 4 = 60 ÷ 4
a = 15
