CREATE TABLE table_name_45 (height__m_ INTEGER, peak VARCHAR(255), class VARCHAR(255), prom__m_ VARCHAR(255))
What is the average height for hewitt class, with prom less than 86, and a Peak of gragareth?
    
SQL: SELECT AVG(height__m_) FROM table_name_45 WHERE class = "hewitt" AND prom__m_ < 86 AND peak = "gragareth"