Suppose you wanted to know the size of black holes with masses that are larger or smaller than the sun. you could go through all the steps in exercise 24.20, wrestling with a lot of large numbers with large exponents. you could be clever, however, and evaluate all the constants in the equation once and then simply vary the mass. you could even express the mass in terms of the sun’s mass and make future calculations really easy. show that the event horizon equation is equivalent to saying that the radius of the event horizon is equal to 3 km times the mass of the black hole in units of the sun’s mass.