The telegram came some minutes after he had left. (past) – все ок! How many pages you will have read by 5 o'clock tomorrow? (future) – вс глагол will в вопросе стоит перед подлежащим. Правильный ответ: How many pages will you have read by 5 o'clock tomorrow? The children already has decided what to do with the books. (Present) – нужно использовать глагол have ( т.к. children – это мн. число) и already стоит между have и decided, правильный ответ: The children have already decided what to do with the books.
I have been waiting for you since two o'clock. - Present By the time he arrives in London, John will have been driving for 5 hours. – здесь future К тому времени как он приедет в Лондон, Джон будет вести машину уже 5 часов. He had a backache. He had been digging the garden. – здесь Past У него были боли в спине. Он копал огород.
Данный ответ на вопрос - It's half past eight (08:30).