What is the percentage of Perdue when McCrory has 37% and Munger has 6%?
CREATE TABLE "opinion_polling_for_the_united_states_gu" (
  "poll_source" text,
  "dates_administered" text,
  "democrat_beverly_perdue" text,
  "republican_pat_mc_crory" text,
  "libertarian_michael_munger" text,
  "lead_margin" real
);
SELECT "democrat_beverly_perdue" FROM "opinion_polling_for_the_united_states_gu" WHERE "republican_pat_mc_crory"='37%' AND "libertarian_michael_munger"='6%';