CREATE TABLE table_42142 ("Call sign" TEXT, "Frequency MHz" FLOAT, "City of license" TEXT, "ERP W" FLOAT, "Class" TEXT, "FCC info" TEXT)

If the call sign is w291ch what's the ERP W corresponding to that sign?
SELECT "ERP W" FROM table_42142 WHERE "Call sign" = 'w291ch'
SELECT "ERP W" FROM "table_42142" WHERE "Call sign" = 'w291ch'