A Microwave radio relay link is to operate in an urban environment over a 20 Km distance at 12GH.The antenna are to be placed a top of two identical buildings at an elevation of 35 m from ground. The local building regulations prohibits construction of buildings higher than 25 m. Determine if it is possible to mount the antennas right at the roof top or if antenna masts to raise the height are needed. In the later case, what should the height of the masts be?