I want to know the answer to the following question:
When did Hou Xian and Zhi Guang return to Nanjing?
All the background I'm provided with is that "Traveling to Lhasa either through Qinghai or via the Silk Road to Khotan, Hou Xian and Zhi Guang did not return to Nanjing until 1407.". Is that enough to answer the question?