Two cars leave the same point simultaneously going in the same direction, along a straight flat road, one at 40 miles per hour and the other at 50 miles per hour. After how many minutes will the cars be 5 miles apart ?

Question

$\begin{array}{1 1} (a)\; \text{30 minutes} \\ (b)\; \text{40 minutes} \\ (c)\; \text{35 minutes} \\ (d)\; \text{25 minutes} \end{array}$