Answer
$3.29h$
Work Step by Step
We know that
$\Delta t=\frac{\Delta Q}{e\sigma A(T^4-T_e^4)}$
We plug in the known values to obtain:
$\Delta t=\frac{306\times 4186}{(0.915)(5.67\times 10^{-8})(1.22)((310.35)^4-(294.95)^4)}$
$\Delta t=11,800\times \frac{1h}{3600s}=3.29h$
