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x in (-oo:+oo)
-((2/5)*x)-5/8 = -31/40 // + -31/40
-((2/5)*x)-5/8-(-31/40) = 0
(-2/5)*x-5/8+31/40 = 0
3/20-2/5*x = 0 // - 3/20
-2/5*x = -3/20 // : -2/5
x = -3/20/(-2/5)
x = 3/8
x = 3/8
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