A positively charged disk of radius R and total charge Q_disk lies in the xz plane, centered on the y axis (see figure below). Also centered on the y axis is a charged ring with the same radius as the disk and total charge Q_ring. The ring is a distance d above the disk. Determine the electric field at the point P on the y axis, where P is above the ring a distance y from the origin. (Use any variable or symbol stated above along with the following as necessary: k.)