A spherical tank, 1 m in diameter, is maintained at a temperature of 120C and exposed to

A spherical tank, 1 m in diameter, is maintained at a temperature of 120ºC and exposed to a convection environment. With h = 25W/m2 ∙ ºC and T∞ = 15ºC, what thickness of urethane foam should be added to ensure that the outer temperature of the insulation does not exceed 40ºC? What percentage reduction in heat loss results from installing this insulation?