Помогите пожалуйста номер 1325

$a^x\ \textgreater \ a^y \Rightarrow \begin{cases} x\ \textgreater \ y , \ a\ \textgreater \ 1 \\ x\ \textless \ y, \ 0\ \textless \ a\ \textless \ 1 \right \end{cases}$

а)
$4^x \leq 64 \\\ 4^x \leq 4^3 \\\ x \leq 3$

б)
$( \frac{1}{2} )^x\ \textgreater \ \frac{1}{8} \\\ ( \frac{1}{2} )^x\ \textgreater \ ( \frac{1}{2} )^3 \\\ x\ \textless \ 3$

в)
$5^x \geq 25 \\\ 5^x \geq 5^2 \\\ x \geq 2$

г)
$( \frac{2}{3} )^x\ \textless \ \frac{8}{27} \\\ ( \frac{2}{3} )^x\ \textless \ ( \frac{2}{3} )^3 \\\ x\ \textgreater \ 3$