SCHEMA:
CREATE TABLE table_name_45 (grid INTEGER, time VARCHAR, bike VARCHAR, laps VARCHAR)
USER:
What is the average Grid for the honda cbr1000rr, with 18 laps and a time of +1:12.884?

QUERY:
SELECT AVG(grid) FROM table_name_45 WHERE bike = "honda cbr1000rr" AND laps = 18 AND time = "+1:12.884"