CREATE TABLE table_18734298_1 (no_in_series VARCHAR, directed_by VARCHAR)

How many series were directed by Rob Renzetti?
SELECT COUNT(no_in_series) FROM table_18734298_1 WHERE directed_by = "Rob Renzetti"
SELECT COUNT("no_in_series") FROM "table_18734298_1" WHERE "Rob Renzetti" = "directed_by"