Table schema:
CREATE TABLE table_name_15 (solidat__ INTEGER, purpose VARCHAR, hardness___brinell__ VARCHAR)

Question: What is the sum of Solidat (c) that's purpose is display type, heavy duty jobs, and a hardness (brinell) is smaller than 33?
SQL: SELECT SUM(solidat__) AS °c_ FROM table_name_15 WHERE purpose = "display type, heavy duty jobs" AND hardness___brinell__ < 33