Find the total time elapsed for a hollow copper sphere of inner radius `3cm` outer radius `6cm`, density `rho = 9 xx 10^(3) kg//m^(3)`, specific heat `s = 4 xx 10^(3) J//kg K` and emissivity `e = 0.4` to cool from `727^(@)C` to `227^(@)C` when the surrounding temperature is `0.K` (for inner surface `e = 1` Stefan's constant `sigma = 5.6 xx 10^(-8) W//m^(2)K^(4))`