Calculating Time Difference from San Francisco and Hong Kong?

Question

I seem to be having some trouble figuring a time difference problem. If a flight arrives in San Francisco from Hong Kong around noon on May 24th, what date and time would it had needed to depart from Hong Kong (in Hong Kong time)?

Answer 1

How fast is the plane flying?

Hong Kong local time (not daylight savings) is 15 hours later in the day than San Francisco local time (which in May is Daylight savings).

i.e., 2:00 am PDT San Francisco is 5:00 pm Hong Kong time the same date