Chaqpter 16 - Temperature and Heat - Problems and Conceptual Exercises - Page 567: 30

$4.3h$

First of all, we convert the radiation rate into calories $62\frac{J}{s}(\frac{1cal}{4186J})=1.481\times 10^{-2}\frac{cal}{s}$ Now we can find the required time $t=\frac{230cal}{1.481\times 10^{-2}\frac{cal}{s}}(\frac{1h}{3600s})=4.3h$