CREATE TABLE table_75620 ("Source" CLOB, "Date" CLOB, "Goldberg" CLOB, "Murray" CLOB, "Silbert" CLOB, "Undecided" CLOB)

What is the date of the poll with Silbert at 18%?
SELECT "Date" FROM table_75620 WHERE "Silbert" = '18%'
SELECT "Date" FROM "table_75620" WHERE "Silbert" = '18%'