Extracting arithmetic mean for specific values from multiple .txt-files

Hello,

I'm coming straight to the point:

I have 65 .txt-Files named "XYZ_1.txt" to "XYZ_65.txt" (each number
represents a test subject).

I have to open them in Microsoft Excel to see the exact structure.

In each of those .txt-files there are reaction time values (in milliseconds)
from line 15, column H to line 166, column H for each test subject (and a
couple of other data in the other colums of course).

My problem is, that I only need the arithmetic mean for all of these
reaction times per test subject.

--> Again: I have 65 test subjects and according to Excel 152 reaction times 
for each test subject / in each .txt-file.

Is there an easy way to only extract the arithmetic mean for each test
subject in an Excel file column?

Thanks for your answers!

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