Джон приступил к работе в 3 часа, а

Джон приступил к работе в 3 часа, а в половине четвертого он ее уже закончил.

Результаты (английский) 1:

John started to work in 3:00, and half of the fourth he has already finished.

Результаты (английский) 2:

John started working at 3 o'clock, and at half past three, he had already finished it.

Результаты (английский) 3:

john began to work for 3 hours, and half of the fourth he already finished.