recall your d = rt, distance = rate * time.
notice, the distance are the same, say it was "d" miles.
and if car A is travelling at a speed of say "r" mph, then B is going at "r+15" mph.
[tex]\bf \begin{array}{lccclll}
&\stackrel{miles}{distance}&\stackrel{mph}{rate}&\stackrel{hours}{time}\\
&------&------&------\\
\textit{Car A}&d&r&2\\
\textit{Car B}&d&r+15&1.5
\end{array}
\\\\\\
\begin{cases}
\boxed{d}=2r\\
d=1.5(r+15)\\
----------\\
\boxed{2r}=1.5(r+15)
\end{cases}
\\\\\\
2r=1.5r+22.5\implies 0.5r=22.5\implies r=\cfrac{22.5}{0.5}\implies \boxed{r=\stackrel{mph}{45}}[/tex]
how far is B going? well, r + 15.
