Two concentric spheres of diameters D₁ = 0.3 m and D₂ = 0.4 m are maintained at uniform temperatures T₁ = 700 K and T₂ = 500 K and have emissivities ε₁ = 0.5 and ε₂ = 0.7, respectively. Determine the net rate of radiation heat transfer between the two spheres. Also, determine the convection heat transfer coefficient at the outer surface if both the surrounding medium and the surrounding surfaces are at 30°C. Assume the emissivity of the outer surface is 0.35.