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2.1*x = 400/5 // - 400/5
2.1*x-(400/5) = 0
2.1*x-80 = 0
2.1*x-80 = 0 // + 80
2.1*x = 80 // : 2.1
x = 80/2.1
x = 38.0952381
x = 38.0952381
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