The city of whitehorse, yukon, receives its maximum amount of sunlight of 19.15 hrs on june 21, and its least amount of sunlight of 5.62 hrs on december 21.

a. due to the earth's revolution about the sun, the hours of daylight function is periodic. determine an equation that can model the hours of daylight function for windsor, ontario.
b. on what day(s) can whitehorse expect 13.5 hours of sunlight?