A 4-m-long section of a 5-cm-diameter horizontal pipe in which a refrigerant flows passes through a room at 20°C. The pipe is not well insulated and the outer surface temperature of the pipe is observed to be 210°C. The emissivity of the pipe surface is 0.85, and the surrounding surfaces are at 15°C. The fraction of heat transferred to the pipe by radiation is
(a) 0.24

(b) 0.30

(c) 0.37

(d) 0.48

(e) 0.58
(For air, use k = 0.02401 W/m ·  K, Pr = 0.735, v = 1.382 × 10^-5 m²/s)