What have you tried so far?
I won't make your homework, but I might give you some hints.

To sort a list/array in perl, we have the sort function, to make it descending numericaly, usually, we'll have something like my @sorted_array = sort {$b <=> $a} @array or my @sorted_array = reverse sort {$a <=> $b} @array. To join something, we'll work with join usually :-) or for more flexible transformations with map. To get some fields seperated by a delimiter, we'd probably use split or in a more complex situation maybe a specialised module like Text::CSV for a CSV-file like your one looks also. So overall, you'll probably just translate your description into some perlish code 1:1 with the above built in ops/functions/modules.