1) What is the minimum mass required for a black hole to form?

2) What is the Mass of the black hole Sagittarius A (at the center of the Milky Way)? (A rough number will work here in terms of solar masses. Please cite a reference to where you obtained the number)

3) Using the escape velocity equation:

v=sqrt (2*G*M/r) where G is the gravitational constant:
G=6.67x10^(-11) m^(3)kg^(-1)s^(-2)

what would the Radius of the black hole at the center of the Milky Way be? When computing this use
A) the escape velocity of a black hole as the speed of light (3x10^8m/s)
B) Mass should be in units of kg to match the units in G

This sounds harder than it looks. Its a "plug and chug" equation.

4) Combining 2 and 3 What is the density of the black hole? Can you compare that to the densest materials that you come into contact with on a daily basis?