A radiation shield that has the same emissivity 3 on both sides is placed between two

A radiation shield that has the same emissivity ε₃ on both sides is placed between two large parallel plates, which are maintained at uniform temperatures of T₁ = 650 K and T₂ = 400 K and have emissivities of ε₁ = 0.6 and ε₂ = 0.9, respectively. Determine the emissivity of the radiation shield if the radiation heat transfer between the plates is to be reduced to 15 percent of that without the radiation shield.