500
Look back at how Hsiang-ling acted when she gave up her purse, and how Mrs. Lu acted when she learned the purse came from Hsiang-ling. Compare and contrast the two actions.
Hsiang-ling gave up her purse because she didn't really need it to go along with her dowry. She also didn't want to have bad luck on her wedding day. She didn't want to be overwhelmed with gratitude for something she considered such a small good deed, one can infer, so she asked that her name not be mentioned.
Mrs. Lu is much more straight forward. She falls to her knees in gratitude and explains exactly how much she owes to Hsiang-ling's generosity. Then she gives Hsiang-ling a huge reward and sends out servants to find her family. She knows who to thank and makes sure she is well rewarded.