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a in (-oo:+oo)
6*(7*a+6) = 204 // - 204
6*(7*a+6)-204 = 0
6*(7*a+6)-204 = 0
42*a-168 = 0
42*a-168 = 0
42*a-168 = 0 // + 168
42*a = 168 // : 42
a = 168/42
a = 4
a = 4
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