I agree with what the lady said before me. I just add the pronounce for you. (你学习中文多久了?ni xue xi zhong wen duo jiu le?) (你学习中文多长时间了? ni xue xi zhong wen duo chang shi jian le?) I am not sure what kind of soundmark you use when you learn Chhinese. Therefore, I just put the soundmark in Chinese way.