$)$ A sinusoidal electromagnetic wave is propagating in vacuum. At a given point P and at a particular time, the electric field is in the $+$x direction and the magnetic field is in the $-$y direction. $($a$)$ What is the direction of propagation of the wave? $($b$)$ If the intensity of the wave at point P is $0\mathrm{.}36$ W$/$m$2,$ what is the electric field amplitude at that point? $($c $=3\mathrm{.}00108$ m$/$s$,$ $0=4$ $10-7$ T $$ m$/$A$,$ $0=8\mathrm{.}8510-12$ C$2/$N $$ m$2)$