Answer
$t=0.554$
Work Step by Step
$4^{-3t}=0.10$
$\log_44^{-3t}=\log_40.10~~$ (Using the Inverse Property: $\log_aa^x=x$):
$-3t=\log_40.10$
$t=-\frac{1}{3}\log_40.10=-\frac{1}{3}\frac{\ln0.10}{\ln4}\approx0.554$
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