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\begin{array}{ll}70=130 e^{-0.0123 t}+35 & \text { Substitute in } 70 \text { for } T(t) . \\35=130 e^{-0.0123 t} & \text { Subtract } 35 . \\\frac{35}{130}=e^{-0.0123 t} & \text { Divide by } 130 . \\\ln \left(\frac{35}{130}\right)=-0.0123 t & \text { Take the natural log of both sides } \\t=\frac{\ln \left(\frac{35}{130}\right)}{-0.0123} \approx 106.68 & \text { Divide by the coefficient of t. }\end{array}