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m in (-oo:+oo)
3/7-((1/3)*m) = -68/21 // + -68/21
3/7-((1/3)*m)-(-68/21) = 0
(-1/3)*m+3/7+68/21 = 0
11/3-1/3*m = 0 // - 11/3
-1/3*m = -11/3 // : -1/3
m = -11/3/(-1/3)
m = 11
m = 11
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