In Exercises $15-22,$ use analytic methods to find $($a$)$ the local extrema, $($b$)$ the intervals on which the function is increasing, and $($c$)$ the intervals on which the function is decreasing.

$15.f(x)=5x-x^2$

$16.g(x)=x^2-x-12$

$17.h(x)=\frac{2}{x}$

$18.k(x)=\frac{1}{x^2}$

$19.f(x)=e^{2x}$

$20.f(x)=e^{-0\mathrm{.}5x}$

$21.y=4-\sqrt[\phantom{2}]{x+2}$

$22.y=x^4-10x^2+9$

Need $17$ and $18$ please