Assuming the Sun to be a spherical body of radius R at a temperature of TK, evaluate the total radiant powered incident of Earth at a distance r from the sun
where `r_0` is the radius of the Earth and `sigma` is Stefan's constant.

Options

A. `4pir_(0)^(2)R^(2)sigma(T^(4))/r^(2)`
B. `pir_(0)^(2)R^(2)sigma(T^(4))/r^(2)`
C. `r_(0)^(2)R^(2)sigma(T^(4))/(4pir^(2))`
D. `R^(2)sigma(T^(4))/r^(2)`