user: Question: How many performers are 29 that made it to the semi finals?
Columns: ['Name/Name of Act', 'Age(s)', 'Genre', 'Act', 'Hometown', 'Semifinal (Week)', 'Position Reached']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['Liu Wei', '23', 'Performing', 'Disabled pianist', 'Huangpu , Shanghai', 1.0, 'Winner']
SQL:

assistant: SELECT COUNT("Semifinal (Week)") FROM "Table" WHERE "Age(s)" = '29';