Nathan lives in London. His older brother Mark lives in San Diego, his younger brother Ben lives in Barcelona and his sister Isabel lives in Nairobi. Nathan is trying to arrange an online call between all four siblings. Each of the siblings has agreed to be available between 08:00 and 20:00 local time. San Diego is 8 hours behind London time. Barcelona is 1 hour ahead of London time. Nairobi is 2 hours ahead of London time.