Fred and Sam are standing 45 miles apart and they start walking in a straight line toward each other at...

$$Total\ relative\ dis\tan ce\ apart=45miles$$
$$Fred's\ speed=4\ miles\ per\ hour$$
$$Sam's\ speed=5\ miles\ per\ hour$$
$$Speed=\frac{dis\tan ce}{timetaken}$$
$$Time\ taken=\frac{dis\tan ce}{speed}$$
$$\sin ce\ both\ Fred\ and\ Sam\ are\ moving\ in\ opposite\ direction;$$
$$their\ relative\ dis\tan ce\ will\ reduce\ at\ their\ combined\ speed=(4+5)mph=9mph$$
$$Time\ taken\ for\ both\ to\ meet=\frac{45}{9}=5hours$$
$$And\ in\ 5\ hours\ at\ Sam's\ speed\ of\ 5miles\ per\ hour;$$
$$dis\tan ce\ covered\ by\ Sam$$
$$=25miles$$
$$Answer=C$$