I was working at six o'clock.
Я работал в шесть часов. I wasn't working at six o'clock.
Я не работал в шесть часов. Was I working at six o'clock?
Я работал в шесть часов?
You were working at six o'clock.
Вы работали в шесть часов. You weren't working at six o'clock.
Вы не работали в шесть часов. Were you working at six o'clock?