Deriving a function/formula from a complete and an incomplete set of Data

I am trying to build a little calculator which suits my personal needs. I want to avoid having to create huge tables of data manually and looking for corresponding values in the table from a given input using lookups. Ultimately I would like to avoid having to create the tables as a whole and only use reference values and let excel derive a formula/function for the rest of the values. This would save time as I would only have to feed function/formula the reference value. I am not trying to plot a graph!

Example 1, Complete set of data:

I have a table with Y-Values and corresponding X-Values. Everything has a linear behaviour except that the point of the 1.0 Mark changes depending on the Y- and X-Values.

So my question is if it is possible for Excel to derive a formula/function from such a set of data which can then be used in a calculation where the input solely consists of the Y- and X-Value and the formula/function will return the correct result? Furthermore I would like to know if I enter a value between say 11 and 12, would this derived formula be able to return the correct value? If not, then it would not be a big deal as I could just round or truncate the input.

Example 2, Limited set of data:

This is the same table as before except that I only have the reference values. Is it possible using those reference values only to derive a formula/function to either populate the table with the data from example 1 or to derive the a formula/function I am trying to get from example 1?

This would basically enable me to change the reference values on the fly and the formula just calculating the rest in the background which would result in much higher flexibility.

Thanks in advance for any pointers/help

-timmeh