Tough but simple physics problem?

A 982 kg probe is to be sent to Ur. Ur has a m of 8.68 x 1025 kg and a radius of 2.56 x 107 m. Scientists want the probe to send back data every 12 hours. To do this they want the probe to orbit around Ur with a period of exactly 12 hours. What should the probe’s orbital radius be? an advice please