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

### Instruction:
How many years have an Opponent in the final of welby van horn?

### Inputs:
table_name: table, columns: ['Outcome', 'Year', 'Championship', 'Surface', 'Opponent in the final', 'Score in the final']

### Response:
SELECT SUM Year FROM table WHERE Opponent in the final = welby van horn