Answer
$40.8 \text{ kilometers/hour}$
Work Step by Step
Let $x$ be the speed of Casper. Then $x+6$ is the speed of Cantador.
Using $D=rt,$ then the conditions of the problem for Cantador is
\begin{array}{l}\require{cancel}
208=(x+6)t
\\\\
\dfrac{208}{x+6}=t
.\end{array}
Using $D=rt,$ then the conditions of the problem for Casper is
\begin{array}{l}\require{cancel}
181.35=xt
\\\\
\dfrac{181.35}{x}=t
.\end{array}
Equating the two equations of $t$ and using the properties of equality result to
\begin{array}{l}\require{cancel}
\dfrac{208}{x+6}=\dfrac{181.35}{x}
\\\\
208(x)=181.35(x+6)
\\\\
208x=181.35x+1088.1
\\\\
208x-181.35x=1088.1
\\\\
26.65x=1088.1
\\\\
x=\dfrac{1088.1}{26.65}
\\\\
x=40.829268292682926829268292682927
.\end{array}
Hence, the speed of Casper, $x,$ (rounded to the nearest tenth) is $
40.8 \text{ kilometers/hour}
.$
