One kilo watt hour is equal to _______J

Question

$\begin{array}{1 1} (a)\; 3.6 \times 10^{6} J \\ (b)\; 3.6 \times 10^{-6}J \\ (c)\; 3.6 \times 10^5 J \\ (d)\; 3.6 \times 10^{-5} J \end{array}$