Two coherent light waves each with intensity $5\mathrm{.}0$ W$/$m$2$ combine. If the phase difference of the two waves is $90,$ what is the resulting intensity?

Group of answer choices

$0$ W$/$m$2$

$5\mathrm{.}0$ W$/$m$2$

$10$ W$/$m$2$

$15$ W$/$m$2$