A recent attempt to circumnavigate the world in a balloon used a helium-filled balloon whose volume was 7240 m³ and surface area was 1800 m². The skin of this balloon is 2 mm thick and is made of a material whose helium diffusion coefficient is 1 × 10^-9 m²/s. The molar concentration of the helium at the inner surface of the balloon skin is 0.2 kmol/m³ and the molar concentration at the outer surface is extremely small. The rate at which helium is lost from this balloon is
(a) 0.26 kg/h

(b) 1.5 kg/h

(c) 2.6 kg/h

(d) 3.8 kg/h

(e) 5.2 kg/h