To do the sorting:

% sort
sorts the input alphanumerically

% sort -n
sorts the input numerically

% sort -k1,1n
sorts using the first field numerically

% sort -k2,2nr
sorts using the second field numerically, reversed


To use grep for the questions:

% grep -n “Martin”
greps for the string Martin, shows line numbers

% egrep -n “<.*>”
greps for HTML tags, shows line numbers