What is the total trip duration made within Palo Alto city? Convert the duration to hour.
total trip duration to hour = DIVIDE(SUM(duration), 3600);
SELECT CAST(SUM(T1.duration) AS REAL) / 3600 FROM trip AS T1 LEFT JOIN station AS T2 ON T2.name = T1.start_station_name WHERE T2.city = 'Palo Alto'