When a cloud passes over a certain spot on the surface of the earth a vertical electric field of E = 100 V/m is recorded there. The bottom of the cloud is a height d = 300m above the earth and the top of the cloud is 600m above the ground. Assume that the cloud is electrically neutral but as a +q at its top and -q at its bottom. Estimate the magnitude of the charge q and the external electric force (direction and magnitude) on the cloud.