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_14 (build_date VARCHAR, prr_class VARCHAR, builder’s_model VARCHAR)
### Question:
When was the build date for ff20 PRR class and erie built builder's model?
### Answer:
SELECT build_date FROM table_name_14 WHERE prr_class = "ff20" AND builder’s_model = "erie built"