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a in (-oo:+oo)
a+3*a-(1/3) = 1/15 // - 1/15
a+3*a-(1/3)-(1/15) = 0
a+3*a-1/3-1/15 = 0
4*a-2/5 = 0 // + 2/5
4*a = 2/5 // : 4
a = 2/5/4
a = 1/10
a = 1/10
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