user: Question: Name the least clock rate mhz when designation is RIMM 4200
Columns: ['Designation', 'Bus width (bits)', 'Channels', 'Clock rate (MHz)', 'Bandwidth (MB/s)']
Types: ['text', 'real', 'text', 'real', 'real']
Sample row: ['PC600', 16.0, 'Single', 266.0, 1066.0]
SQL:

assistant: SELECT MIN("Clock rate (MHz)") FROM "Table" WHERE "Designation" = 'RIMM 4200';