Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_98 (casting_at__°c_ VARCHAR, hardness VARCHAR)
### Question:
What is the casting temperature for the alloy with hardness 21?
### Answer:
SELECT casting_at__°c_ FROM table_name_98 WHERE hardness = "21"