Below is an instruction that describes a task. Write a response that appropriately completes the request.

### Instruction:
What year was the carriage type is 47' 6" 'birdcage' gallery coach built

### Inputs:
table_name: table, columns: ['Number', 'TMS Number', 'Builder', 'Year built', 'Carriage type']

### Response:
SELECT Year built FROM table WHERE Carriage type = 47' 6" 'Birdcage' gallery coach