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a in (-oo:+oo)
6-(4*a)-a = 66 // - 66
6-(4*a)-a-66 = 0
6-4*a-a-66 = 0
-5*a-60 = 0 // + 60
-5*a = 60 // : -5
a = 60/(-5)
a = -12
a = -12
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