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Designed a thin square radiator fin made of copper for cooling a device

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Designed a thin square radiator fin made of copper for cooling a device. Each of the two flat surfaces is 9.0 cm^2 , and the fin has mass of 2.7 g. Copper has a specific heat capacity of 386 J/kg/K, and a density of 8750 kg/m3 . It normally operates at a temperature of 65 C.

a) Show that the surface area of the sides of the fin are negligible compared to the surface area of the front and back and lower surfaces.

b) Calculate the power lost due to radiation, assuming it is a black body emitter with an emissivity e = 0.97

c) Calculate the power lost due to convection, assuming only natural air circulation, with h = 25 W/m2 and an air temperature of 25 C

d) Calculate the power lost due to forced air circulation with a fan, and h = 325.

e) Suppose the power that the fin needs to dissipate from the device is 7.8 Watts, and the air circulation fan fails. How long will the fin take to heat up from the normal operating temperature 65 C, to 95 C?