[tex]\bf \begin{cases}
m=\textit{Missy's amount of books}\\
j=\textit{Justin's amount of books}\\
a=\textit{Andrew's amount of books}
\end{cases}\\\\
-----------------------------\\\\
\textit{we know "m" is three times as much as "j"}\implies m=3j
\\\\\\
\textit{we also know, "j" is two fewer than "a"}\implies j=a-2
\\\\\\
\textit{their sum is 17}\implies m+a+j=17\\\\
-----------------------------\\\\
\begin{cases}
m=3j\\
j=a-2\implies j+2=a\\
----------\\
m+a+j=17\\
(3j)+(j+2)+j=17
\end{cases}[/tex]
solve for "j"
