Mark drove to his office at 60 miles per hour. Returning over the same route, to his home, he encountered heavy traffic and was able to drive at only 40 miles per hour. If the return trip took 1 hour longer, how many miles did he drive each way ?

Question

$\begin{array}{1 1} (a)\; 20 \\ (b)\; 30 \\ (c)\; 50 \\ (d)\; 120 \end{array}$