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x in (-oo:+oo)
3/8-(7*x) = 3 // - 3
3/8-(7*x)-3 = 0
3/8-7*x-3 = 0
-7*x-21/8 = 0 // + 21/8
-7*x = 21/8 // : -7
x = 21/8/(-7)
x = -3/8
x = -3/8
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