The value of $k$ if $x=-a$ is a solution of the equation $x^2+2ax-k=0$ is _______

Question

$\begin{array}{1 1}(A) \; k=a^2\\(B)\;k=-a^2 \\(C)\;k=\pm a^2 \\(D)\;\text{None of the above} \end{array}$