Extrapolation interpolation proportion?

Connect all the data points using a smooth line. For an example, see here:

http://www.docstoc.com/docs/4871801/Read...

Extrapolate:

From your last data point, extend the graph past 100 degrees in the same general manner as it has behaved when you drew the line connecting the actual data points. read the graph line at 100 degress for the quantity of NH4Cl

Interpolate:

50 degrees was not one of your data points. After you have drawn the line using your data points, read the graph at 50 degrees.

Basically, E is when you are extending the graph past your last data point and I is reading a data point that is within the set of your actual data points, but is not one of the actual data points that was experimentially measured.

Proportion:

Use an actual data point close to 30 degrees.

Actual quantity is to actual temperature as x is to 30 degrees

Another way to write this is:

Actual quantity / actual temperature = x i/ 30 degrees

This was one of the questions asked on Yahoo Answers, and from what I know, the answer is correct.