user: Question: What is the quantity preserved for the serial number of Mallet and Simple Articulated Locomotives?
Columns: ['Class', 'Wheel arrangement', 'Fleet number(s)', 'Manufacturer', 'Serial numbers', 'Year made', 'Quantity made', 'Quantity preserved']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Mallet and Simple Articulated Locomotives', 'Mallet and Simple Articulated Locomotives', 'Mallet and Simple Articulated Locomotives', 'Mallet and Simple Articulated Locomotives', 'Mallet and Simple Articulated Locomotives', 'Mallet and Simple Articulated Locomotives', 'Mallet and Simple Articulated Locomotives', 'Mallet and Simple Articulated Locomotives']
SQL:

assistant: SELECT "Quantity preserved" FROM "Table" WHERE "Serial numbers" = 'Mallet and Simple Articulated Locomotives';