CREATE TABLE table_name_18 (frequency__per_hour_ VARCHAR2, line VARCHAR2, destination VARCHAR2)

How many frequencies have a line of East London and destination of Crystal Palace?
SELECT COUNT(frequency__per_hour_) FROM table_name_18 WHERE line = "east london" AND destination = "crystal palace"
SELECT COUNT("frequency__per_hour_") FROM "table_name_18" WHERE "crystal palace" = "destination" AND "east london" = "line"