Answer
$t = 2.6\times 10^4~years$
Work Step by Step
In part (b), we found that the amount of energy released is $8.2\times 10^{13}~J$
We can find the time that this energy could light a 100 W lamp:
$t = \frac{8.2\times 10^{13}~J}{100~W}$
$t = 8.2\times 10^{11}~s$
$t = (8.2\times 10^{11}~s)[\frac{1~year}{(365)(24)(3600~s)}]$
$t = 2.6\times 10^4~years$
