Iain’s car has run out of petrol. He walks 12 km west and then 9 km south looking for a petrol station.

If he is now $h$ km directly from his starting point, find the value of $h$.
Please directly answer the question and provide the final value, e.g., 1, 2.5, 300.
Question: Iain’s car has run out of petrol. He walks 12 km west and then 9 km south looking for a petrol station.

If he is now $h$ km directly from his starting point, find the value of $h$.
Please first conduct reasoning, and then answer the question and provide the final value, e.g., 1, 2.5, 300, at the end.
Question: Iain’s car has run out of petrol. He walks 12 km west and then 9 km south looking for a petrol station.

If he is now $h$ km directly from his starting point, find the value of $h$.