a) The angle that a nebula appears in the sky increases by 0.05 arc seconds per year. From the Doppler shift, it is determined that the gas is expanding at 800km/s. Find the distance from Earth to this nebula. b) This nebula has an angular size of 5 arc minutes today. Assuming the gas has always been expanding at a constant speed (800km/s), determine how long ago the star exploded. c) The gas's total mass is 10 solar masses, and the original star had a luminosity of 104 Lsun. What is the kinetic energy of the gas? How long would the star have had to shine to produce the same amount of energy?