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a in (-oo:+oo)
66 = 3*a+4*a+3 // - 3*a+4*a+3
66-(3*a)-(4*a)-3 = 0
66-3*a-4*a-3 = 0
63-7*a = 0 // - 63
-7*a = -63 // : -7
a = -63/(-7)
a = 9
a = 9
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