A portable heater is placed inside a laboratory chamber to maintain the inside air temperature of the chamber at 38°C. The chamber is spherical with the inner radius measuring 35 cm. The wall is 1.2 cm thick and is made of polystyrene (k = 0.028 W/m-°C). The laboratory chamber is placed in a convection environment of 21°C. The inside and outside heat transfer coefficients are 5 and 22 W/m2-°C, respectively. Determine the heat generation rate of the portable heater. What are the temperatures at the inner and outer surfaces of the laboratory chamber?