after dudley of mrs. figg's broken leg, why did he pretend to cry

I'm sorry, I do not understand your question as asked. Please rephrase or correct your post.

he cries because he does no t like his babysitter, mrs. figg

If I am not mistaken, Mrs. Figg was supposed to babysit Harry Potter while the Dursleys went to the zoo for Dudley's birthday. She had broken her leg, therefore she could not babysit Harry. Dudley was crying because it meant that Harry would have no option but to go the the zoo, and Dudley did not want that because he despised Harry.