How many weeks are shown for the champion of john mcenroe 6–2, 6–3?
CREATE TABLE "table1_21584646_10" (
  "week_of" text,
  "tournament" text,
  "champion" text,
  "runner_up" text,
  "semifinalists" text,
  "quarterfinalists" text
);
SELECT COUNT("week_of") FROM "table1_21584646_10" WHERE "champion"='John McEnroe 6–2, 6–3';