届く and 届ける: arrival, reach, and handing in lost property
Compare a parcel arriving with delivering it, and distinguish physical reach from handing in lost property.
An arrived item and its delivery
注文した本が今日届きました。 means that the ordered book arrived today. With 届く, read とどく, the arriving book is the subject.
配達員が荷物を玄関まで届けてくれました。 says that the delivery person brought the package to the entrance for the speaker. 届ける, read とどける, specifies the delivered item and how far it was brought.
Something within reach
背伸びしても、上の棚に手が届きません。 means that even standing on tiptoe, the speaker cannot reach the upper shelf. 手が is the subject and 棚に is the point being reached for.
ここから声が届きますか。 asks whether the speaker's voice carries from here. This concerns the reach of sound, not delivery of a parcel.
Take lost property to the responsible person
拾った財布を交番に届けました。 says that someone handed a found wallet in at a police box. 財布を is the object and 交番に is where it was taken.
届く becomes 届きます and 届いて; 届ける becomes 届けます and 届けて. Distinguish arrival from delivery using the particles as well as these similar-looking forms.
What fails to reach the target in 上の棚に手が届きません?
Show the answer and why
The person's hand cannot reach the upper shelf. 手 is the subject, and 上の棚に is the target; it does not concern an inability to deliver a shelf.