The amplitude is 80-75 = 5 degrees. The period is 24 hours. We want represent the function as the sine function. So, we will start the period at (1/4) of 24 hours before 5 pm. Hence, the start for the period is 11 am. Now the general formula is T(t) = 5*sin(2*pi*((t-11)/24)) + 75, where t is the time (in hours) on the clock during the day in 24-hours military notation. In particular, at t = 9 am the temperature is T(9 am) == = = = = = = 75 - 2.5 = 72.5 degrees. ANSWER