For the first one:
[tex]\begin{gathered} 28-\log _2(x-3)=9 \\ \rightarrow28-9=\log _2(x-3)\rightarrow19=\log _2(x-3) \end{gathered}[/tex]
Remember that:
[tex]\log _a(b)=c\Leftrightarrow a^c=b[/tex]
This way,
[tex]\begin{gathered} 19=\log _2(x-3)\leftrightarrow2^{19}=x-3\rightarrow2^{19}+3=x \\ \rightarrow x=524291 \end{gathered}[/tex]
For the last one:
[tex]\begin{gathered} 200000=100000e^{0.08t} \\ \rightarrow\ln (200000)=\ln (100000e^{0.08t}) \\ \rightarrow\ln (200000)=\ln (100000)+\ln (e^{0.08t}) \\ \rightarrow\ln (200000)-\ln (100000)=(0.08t)\ln (e^{}) \\ \rightarrow\ln (200000)-\ln (100000)=0.08t \\ \rightarrow\frac{\ln (200000)-\ln (100000)}{0.08}=t \\ \rightarrow t=8.66 \end{gathered}[/tex]
