How many numbers were listed under Silver Medals for Portsmouth HS?
CREATE TABLE "percussion_scholastic_concert_open_class" (
  "ensemble" text,
  "gold_medals" real,
  "silver_medals" real,
  "bronze_medals" real,
  "total_medals" real
);
SELECT COUNT("silver_medals") FROM "percussion_scholastic_concert_open_class" WHERE "ensemble"='Portsmouth HS';