What is the last year that Howard A. Wassum was in the 5th district?
CREATE TABLE "supervisors" (
  "year" real,
  "1st_district" text,
  "2nd_district" text,
  "3rd_district" text,
  "4th_district" text,
  "5th_district" text
);
SELECT MAX("year") FROM "supervisors" WHERE "5th_district"='Howard A. Wassum';