How to select specific cells among thousands of cells that are in one column?

Hello All,

Just in summary of the problem i am having is as follows:

- I have one column that contains thousands of cells (data);

- what i want to achieve is the average of some specific cells in the column;

- my problem is that i cannot select one by one as it is impossible and they are not any type of order;

- what i have is the row number (e.g. 604, 1122,...,) and the column letter;

- I want to take the average of these cells without taking in consideration the others in the same column (e.g. how to pick these cells automatically since i know their column letter and their row number)

The excel file is attached :

Column A is the data column, where i want to take the average from

Column C is the row numbers of the cell's that i want to the average of.

Thank you very much for your kind help.

Kind regards,

Salam