recall your d = rt, distance = rate * time.
let's say the Eastbound train is going at a rate of "r" mph, since we know the Westbound train is going faster 12 miles more than that, then the Westbound train must be going "r+12".
we also know that after 4 hours, both of them were 760 miles apart, so
[tex]\bf \begin{array}{lccclll}
&\stackrel{miles}{distance}&\stackrel{mph}{rate}&\stackrel{hours}{time}\\
&------&------&------\\
Westbound&760&r+12&4\\
Eastbound&760&r&4
\end{array}
\\\\\\
\begin{cases}
760=(r+12)(4)\implies 190=r+12\\
760=4r\implies 190=r
\end{cases}
\\\\\\
\textit{since we know that r = 190, then }\qquad \stackrel{Westbound}{190+12}[/tex]
