9.
\(10.\left(1+4\%\right)^8=13,686\)
10.
\(100.\left(\dfrac{1}{2}\right)^{\dfrac{t}{138}}\le25\)
\(\Rightarrow\dfrac{t}{138}\ge2\)
\(\Rightarrow t\ge276\)
12.
\(130>10log\left(\dfrac{I}{I_0}\right)\Rightarrow\dfrac{I}{I_0}< 10^{13}\)
\(\Rightarrow I< I_0.10^{13}=10\)