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m in (-oo:+oo)
m/5+m/3 = 13 // - 13
m/5+m/3-13 = 0
8/15*m-13 = 0 // + 13
8/15*m = 13 // : 8/15
m = 13/8/15
m = 195/8
m = 195/8
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