An electromagnetic wave with frequency 4.00 x 1014 Hz travels through vacuum in the positive direction of an x axis. The wave has its electric field directed parallel to the y axis, with amplitude E m. At time t = 0, the electric field at point P on the x axis has a value of + E m/4 and is decreasing with time. What is the distance along the x axis from point P to the first point with E = 0 if we search in
(a) The negative direction and
(b) The positive direction of the x axis?