How do I do this with "filter" or "map" but without using lambda? Please explain this step-by-step. Thanks

Write a function longest_s_word that takes a list of strings and returns the longest string in the list that starts with "S" or "S". If there is a tie, it should return the one at the earliest index. If there is no word that starts with "s" or "S", it should return the empty string. Example: >>> longest_s_word ( ["surf", "salad", "agree"]) 'salad