Answer
(a) $E = 262~J$
(b) $P = 8.1\times 10^{-3}~W$
Work Step by Step
(a) We can find the total charge:
$Q = I \times t$
$Q = (18.0\times 10^{-3}~A)(9.0~h)(\frac{3600~s}{1.0~h})$
$Q = 583.2~C$
We can find the energy supplied by the solar cell:
$E = V~Q$
$E = (0.45~V)(583.2~C)$
$E = 262~J$
(b) We can find the power:
$P = \frac{Energy}{time} = \frac{262~J}{(9.0~h)(3600~s/h)} = 8.1\times 10^{-3}~W$
