How do I calculate values from a chart?

Newbie here! So please be kind if I am posting in the wrong forum!

I have a series of numbers (X and Y) from which I create a chart from as shown on the attached Excel spreadsheet. The chart is the smooth line type available in Excel.

The question is, how do I find the Y value corresponding to a given X? Basically if X is given I need to be able to calculate the corresponding Y.

Thank you all for your HELP! I greatly appreciate any assistance as I am currently stuck in what I am doing and need to get this solved!