Two concentric cylinders of diameters D_i = 30 cm and D_o = 40 cm and length L = 5 m are separated by air at 1 atm pressure. Heat is generated within the inner cylinder uniformly at a rate of 1100 W/m³, and the inner surface temperature of the outer cylinder is 300 K. The steady–state outer surface temperature of the inner cylinder is
(a) 402 K

(b) 415 K

(c) 429 K

(d) 442 K

(e) 456 K
(For air, use k = 0.03095 W/m · K, Pr = 0.7111, v = 2.306 × 10^-5 m²/s)