Aditya's dog routinely eats Aditya's leftovers, which vary seasonally. As a result, his weight fluctuates

throughout the year.

The dog's weight W(t) (in kg) as a function of time t (in days) over the course of a year can be modeled by

a sinusoidal expression of the form a. cos(b. t) + d.

Att = 0, the start of the year, he is at his maximum weight of 9.1 kg. One-quarter of the year later, when

t = 91.25, he is at his average weight of 8.2 kg.

Find W(t).

t should be in radians.

W(t) =