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42-((2/5)*x) = 30 // - 30
42-((2/5)*x)-30 = 0
(-2/5)*x-30+42 = 0
12-2/5*x = 0 // - 12
-2/5*x = -12 // : -2/5
x = -12/(-2/5)
x = 30
x = 30
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