Tell me the total number of years for lady cecily waynflete and opera house, kennedy center
CREATE TABLE "theater_credits" (
  "year" real,
  "play" text,
  "role" text,
  "theatre" text,
  "location" text
);
SELECT COUNT("year") FROM "theater_credits" WHERE "role"='lady cecily waynflete' AND "theatre"='opera house, kennedy center';