CREATE TABLE table_name_34 (laps NUMBER, driver VARCHAR2, grid VARCHAR2)

what's the highest lap that contains the driver of graham hill and a grid that is larger than 18?
SELECT MAX(laps) FROM table_name_34 WHERE driver = "graham hill" AND grid > 18
SELECT MAX("laps") FROM "table_name_34" WHERE "driver" = "graham hill" AND "grid" > 18