Analyzing data for this lab wasn't too bad, once I figured out how to use spreadsheets (Emma helped me!)

First, I put in all the data values. Then, I used the derived formula for k in my procedure : 

To solve for k at each data point. Then, I averaged them for each liquid. 

Here's the spreadsheet for salt water:

The one for oil:

And the one for plain water:

You can also see how the different K's manifest themselves in the cooling curves for each liquid.

So what do these show?

Water had the highest k value. Salt water's was about 80% of water's, and the k for oil was about half of that of salt water! This means that the rate at which oil cools depends less on temperature difference than the rates at which salt water and water cool, respectively. This shows a different specific heat as well.

Why were the salt water and water ones different? Adding a solute to a solvent (in this case, salt to water) alters the molecular bonds between water molecules. This causes boiling point elevation and freezing point depression, and also clearly interferes with the way the liquid cools. 

 I didn't really extend the graphs to a large enough t to show asymptotic behavior, but all of the graphs would have the same asymptote- the ambient temperature. Anything put in a surrounding temperature cannot get cooler than the surrounding temperature by cooling.