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x in (-oo:+oo)
3/8-((4/5)*x) = -1/40 // + -1/40
3/8-((4/5)*x)-(-1/40) = 0
(-4/5)*x+3/8+1/40 = 0
2/5-4/5*x = 0 // - 2/5
-4/5*x = -2/5 // : -4/5
x = -2/5/(-4/5)
x = 1/2
x = 1/2
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