How Do You Calculate Time When You Know The Distance And Speed?

The way my physics teacher at school told me to do a calculation of this kind was to remember this visual pyramid (its not great as I've had to type it out):
^
___Distance___
Speed X Time

Then, when you have a missing value, you just need to do what the pyramid says. So if you have the values for speed and time, then as they are next to each other on the pyramid, you times them together:
^
____????____
Speed X Time

= Speed X Time = Distance

And if you have one of the lower values missing, then you divide top by bottom:

^
___Distance___
???? X Time

= distance/time = speed

Or:
^
___Distance___
Speed X ????

= Distance/Speed = Time

All you really have to remember then is that distance has to be on top of the pyramid, and that you either divide or times depending on what values you have at hand.

Hope this helps!!