Пять часов уже (прошли - прошло) после твоего звонка
как правильно написать это предложение

як знайти 1/2 від 28 ????

1)    Как определить, какое окончание следует писать у имени прела -                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       гательного в безударном положении?-