CREATE TABLE table_39418 ("Call sign" TEXT, "Frequency MHz" FLOAT, "City of license" TEXT, "ERP W" FLOAT, "Class" TEXT, "FCC info" TEXT)

What class is assigned to frequencies lower than 90.5?
SELECT "Class" FROM table_39418 WHERE "Frequency MHz" < '90.5'
SELECT "Class" FROM "table_39418" WHERE "Frequency MHz" < '90.5'