As described, the curve is decreasing at t = 0 (that is, at midnight), vewry shortly reaching its minimum and then increasing to its maximum. It is up to you whether you use a sine curve shifted far to the left or a cosine curve shifted a little to the right.
If the high and low points of the curve are twelve hours apart, then what is the period (from high to low, and then back to high)?
If the maximum is 103 and the minimum is 65, then what is the amplitude? What is the vertical shift (so that this amplitude is "centered" correctly)?
If the minimum occurred at t = 4, then what is the phase shift, given the above period?
If you get stuck, please reply showing your work and reasoning so far. Thank you!