getrc is really two problems in one:

(1) Given a row and a column, extract the corresponding value from a simple CSV (comma separated values) file.
(2) Given an argument like "3,4", get the 3 at one point and get the 4 later.

First, try writing "getrc ROW COL"--two arguments instead of one:

    % getrc 1 2 a3/getrc.1
    b
    
    % getrc 3 1 a3/getrc.1
    e

Next, try writing "getrownum R,C":
    
    % getrownum 3,4
    3
    
    % getrownum one,two
    one

Then, see if you can combine those two solutions.