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**e^(i*pi)** Use Newton's Law of Cooling:

$\displaystyle \frac{dT}{dt} = -kT$

which when integrated gives:

$\displaystyle T = T_{0}e^{-kt}$ where $\displaystyle T$ is final temperature, $\displaystyle T_{0}$ is initial temperature, $\displaystyle k$ is a constant and $\displaystyle t$ is time

Plug in what you know:

$\displaystyle

215 = 375e^(-15k)$

$\displaystyle

k = -\frac{1}{15}ln{\frac{215}{375}}$

Now we know k we can use it to find t:

$\displaystyle t = -\frac{1}{k}ln({\frac{T}{T_{0}})} = -\frac{1}{\frac{1}{15}ln{\frac{215}{375}}}ln({\frac {120}{375})}$