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

### Instruction:
This engine with a cylinder size of 20 ½” x 26” and a firebox of radial-stay was built when?

### Inputs:
table_name: table, columns: ['Class', 'Firebox', 'Cylinder size', 'Valves', 'Valve gear', 'Number built', 'Years built']

### Response:
SELECT Years built FROM table WHERE Cylinder size = 20 ½” x 26” AND Firebox = Radial-stay