Cathy walked to school at an average speed of 2.5 miles per hour and jogged back along the same route at an average speed of 6 miles per hour. If her total travelling time was 1.5 hours, what was the total number of miles in the round trip ?

Question

$\begin{array}{1 1} (a)\; 6.75 \;miles \\ (b)\; 10.50\;miles\\ (c)\; 12.50\;miles \\ (d)\; 12.75\;miles \end{array}$