Answer: 870 W/m²
Step-by-step explanation:
Using Fourier's Law of Heat Conduction, the rate of heat transfer per unit area (q) can be calculated as:
q = k × (T1 - T2) / L
where k is the thermal conductivity of the material, T1 is the temperature of the warmer, T2 is the temperature of the surrounding environment, and L is the thickness of the material.
Plugging in the given values, we get:
q = 29 W/m·K × (40°C - 20°C) / (20 mm / 1000)
q = 870 W/m²
Therefore, the rate of heat transfer per unit area of the surface is 870 W/m².