Answer:


Step-by-step explanation:
a) Let the average kinetic energy = gravitational potential energy
Then; by equation :

here;
m = mass of the confined photons
= escape velocity
M = mass of the star
R = radius



b) Let
(where c = speed of light)


where
R =

By using the expression ;
and

Then;


since (
)
Replacing m for M in
; we have:



