Try this. Here test.txt is the name of your file. This code will create a new file and save the sums in it.
data = fileread('test.txt');
data = strrep(data, ',', '.');
num_data = sscanf(data, '%f\n');
sum_6 = sum(reshape(num_data, 6, []), 1)';
f = fopen('new_file.txt', 'w');
fprintf(f, '%1.2f\n', sum_6);
fclose(f);
