Question: How many trips started from Mountain View city and ended at Palo Alto city?
SQL: SELECT count(*) FROM station AS T1 JOIN trip AS T2 JOIN station AS T3 JOIN trip AS T4 ON T1.id  =  T2.start_station_id AND T2.id  =  T4.id AND T3.id  =  T4.end_station_id WHERE T1.city  =  "Mountain View" AND T3.city  =  "Palo Alto"