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(3/5)*(20-x) = (-4/5)*(2*x+15) // - (-4/5)*(2*x+15)
(3/5)*(20-x)-((-4/5)*(2*x+15)) = 0
(3/5)*(20-x)+(4/5)*(2*x+15) = 0
3/5*(20-x)+4/5*(2*x+15) = 0
3/5*(20-x)+4/5*(2*x+15) = 0
x+24 = 0
x+24 = 0
x+24 = 0 // - 24
x = -24
x = -24
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