What would be the average luminosity of the accretion disk, if it continuously radiated that energy over a period of 12 billion years?

The average luminosity can be calculated as E/delta t , where E is the total amount of energy radiated by the accretion disk: E=mc^2. m is the mass of the accretion disk, c is the the speed of light. Delta t is known from the question delta t = 12 billion years. Unknown is the mass of the accretion disk and this mass depends on the type of the accretion disk.

jupiter is the largest planet in our solar system, having a mass and radius that are respectively, 318 and 11.2 times that of earth. suppose that an object falls from rest near the surface of each planet and that the acceleration due to gravity remains constant during the fall. each object falls the same distance before striking the ground. determine the ratio of the time of fall on jupiter to that on earth.