Two coherent light waves each with intensity $5\mathrm{.}0\frac{W}{m^2}$ combine. If the phase difference of the two waves is $60,$ what is the resulting intensity?

$0\frac{W}{m^2}$

$5\mathrm{.}0\frac{W}{m^2}$

$10\frac{W}{m^2}$

$15\frac{W}{m^2}$