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_142573_1 (clock_rate__mhz_ INTEGER, designation VARCHAR)
### Question:
Name the least clock rate mhz when designation is rimm 4200
### Answer:
SELECT MIN(clock_rate__mhz_) FROM table_142573_1 WHERE designation = "RIMM 4200"