A bug flies toward a pile of food.  He starts out 7 meters from the food, and he can fly at .75 m/s.  How long will it take to get there?

This is easy: Since s=d/t, then t=d/s, so t=(7m)/(.75m/s)=9.33seconds.

A second bug also noticed from 10m away the food at the same time the first bug did.  She flies at .5m/s toward it.  How long does the first fly have uninterrupted dining?

Her time is given by t=d/s=(10m)/(.5m/s)=20seconds.  So he gets there first, then she arrives 20-9.33=10.67seconds later.

The two bugs both leave the food pile at the same time and fly in opposite directions.  How far apart will they be at 15 seconds?

The answer is HIS DISTANCE + HER DISTANCE.  Distance is given by d=t*s, so his distance=15s*.75m/s=11.25m and her distance is 15s*.5m/s=7.5m ; the answer is then 18.75m

You can probably imagine that these problems could get more difficult.  To solve them, first try to visualize the situation.  Next try to see what will give you the answer you are looking for.
Click here, login, and in chapter 1 solve the problem called "distance1"