Calculate the maximum range when radar operates at 10GHz and has peak power=10 Mwatt,S/N ratio=10dB,antenna cross section=100 mm2,target cross section=10mm2.The gain of transmitting antenna is 15dB.

I'm not going to do your homework for you, but you should be aware that there are additional factors that reduce the maximum range of a radar. The Pulse Repitition Frequency limits the maximum range because it allows signal returns only from a certain distance before the transceiver stop listening and starts transmitting the next pulse. Also, if this is a rotating surveillance radar, then the antenna rotation speed limits the maximum range, because the antenna might have moved too far before signals can return from long distances. This is why long range radar antennas turn slowly.