(1) Before going home, you must meet the requirements of (20-10.4)/120× 300 ≤ 20, and if you want to consider the automatic alarm of cars with fuel less than 3L, you must meet the requirements.

(20-10.4)/120× 300 ≤ 20-3 Go home. It can be concluded from the inequality above that you can't drive home.

(2) (20-10.4)/120× 300-20+3 Because we have to go home before calling the police, there must be at least 3L of oil left in the mailbox when we get home.