We have the following:
[tex]\begin{gathered} d=v\cdot t \\ v=\frac{d}{t} \end{gathered}[/tex]replacing, d = 523 miles and t = 11.5 hours:
[tex]\begin{gathered} v=\frac{523}{11.5} \\ v=45.48 \end{gathered}[/tex]The average speed is 45.48 miles per hour