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t in (-oo:+oo)
3*(7-(7*t)) = 147 // - 147
3*(7-(7*t))-147 = 0
3*(7-7*t)-147 = 0
3*(7-7*t)-147 = 0
-21*t-126 = 0
-21*t-126 = 0
-21*t-126 = 0 // + 126
-21*t = 126 // : -21
t = 126/(-21)
t = -6
t = -6
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