Pluto's distance from the sun varies in a periodic way that can be modeled approximately by a trigonometric function. Pluto's maximum distance from the sun (aphelion) is 7.47.47, point, 4 billion kilometers. Its minimum distance from the sun (perihelion) is 4.44.44, point, 4 billion kilometers. Pluto last reached its perihelion in the year 198919891989, and will next reach its perihelion in 223722372237. Find the formula of the trigonometric function that models Pluto's distance DDD from the sun (in billion \text{km}kmstart text, k, m, end text) ttt years after 200020002000. Define the function using radians.