Stefan-Boltzmann law

The Stefan-Boltzmann law can be employed to estimate the rate of radiation of energy H from a surface, as in
H = Aeσ T 4
where H is in watts, A = the surface area (m2), e = the emissivity that characterizes the emitting properties of the surface (dimensionless), σ = a universal constant called the Stefan-Boltzmann constant (= 5.67 × 10−8 Wm−2K−4), and T = absolute temperature (K). Determine the error of H for a steel plate with A = 0.15m2, e = 0.90, and T = 650 ± 20. Compare your results with the exact error. Repeat the computation but with T = 650 ± 40. Interpret your results.