The 40-cm-thick roof of a large room made of concrete (k = 0.79 W/m · K, α = 5.88 × 10^-7 m²/s) is initially at a uniform temperature of 15°C. After a heavy snow storm, the outer surface of the roof remains covered with snow at 25°C. The roof temperature at 18.2 cm distance from the outer surface after a period of 2 hours is
(a) 14°C

(b) 12.5°C

(c) 7.8°C

(d) 0°C

(e) 25°C