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(-1/3)*x-((2/7)*x)+7/10 = 213/490 // - 213/490
(-1/3)*x-((2/7)*x)+7/10-(213/490) = 0
(-1/3)*x+(-2/7)*x+7/10-213/490 = 0
13/49-13/21*x = 0 // - 13/49
-13/21*x = -13/49 // : -13/21
x = -13/49/(-13/21)
x = 3/7
x = 3/7
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