If $x^2+y^2=16$, and $xy=4$, what can be the value of $x+y$ ?

Question

$\begin{array}{1 1} (a)\; 6\sqrt{2} \\ (b)\; 4\sqrt{2} \\ (c)\;2\sqrt{6} \\ (d)\; 4\sqrt{6} \end{array}$