A hot plane surface at 100°C is exposed to air at 25°C with a combined heat transfer coefficient of 20 W/m² · K. The heat loss from the surface is to be reduced by half by covering it with sufficient insulation with a thermal conductivity of 0.10 W/m · K. Assuming the heat transfer coefficient to remain constant, the required thickness of insulation is
(a) 0.1 cm

(b) 0.5 cm

(c) 1.0 cm

(d) 2.0 cm

(e) 5 cm