How to find the y-values corresponding to new x-values from a graph

[es20g13]

I have this data, which corresponds to x-values from 0->29.53 (in days) in intervals of 0.01 as shown on the excel spreadsheet attached, on the 1st Sheet. I have the graph plotted in the spreadsheet using scatter with lines of best fit.

Now from the same data/graph, I need to find the Y-values for a new set of x values given in the 2nd sheet of the attachment. Does anyone know a simple way of doing this? The values still go up from 0->29.53 in intervals 0.0035 or so, but be warned they are inconsistent and skip a couple of times every so often. I have checked and seen that people have linearly interpolated, which is effective for a few data points, but as you can see there on my graph multiple trend lines so trend functions and forecast functions won't work either.

Here's the link to the spreadsheet: https://drive.google.com/open?id=0B9...FlPRWpUWnRlS3c

If you need more clarity on what it is I need, please don't hesitate to ask. Appreciate all help provided, Thanks in advance!

[zbor]

Find the equation of a line given by two nearby points and then linear extrapolate.

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Might look complicated formula but principle is easy.
You just need to fin each x1, x2, y1, y2 with INDEX/MATCH combination