Evaluate composite functions

$\begin{aligned} g \circ f(0.64) & = g(f({\color{#3D99F6}0.64})) = g\left(\sqrt{\color{#3D99F6}0.64}\right) = g({\color{#D61F06}0.8}) = \frac 1{\color{#D61F06}0.8} = \boxed{1.25} \end{aligned}$

Let's evaluate $f(0.64)$

$f(a)=√a$

$f(0.64)=√0.64$

= $\dfrac{√64}{√100}$

= $\dfrac{8}{10}$

= $\dfrac{4}{5}$

we know that $g(f(0.64)$ ) is the same as

$g(\dfrac{4}{5})$ because $f(0.64)$ = $\dfrac{4}{5}$

so now let's evaluate $g(\dfrac{4}{5})$

$g(b)$ = $\dfrac{1}{b}$

$g(\frac{4}{5})$ = $\dfrac{5}{4}$

so, $(gof)(0.64)$ = $\dfrac{5}{4}$

or, \color\red{1.25}