Duration time I can live in China.

It depends, visa officers have the final say to decide your visa type and duration. The invitation letter is only a support.

Hello I am sri lankan married to Chinese living in Shanghai I can explain you well your letter must be authorize forehand before going to the embassy but this seal is not able to get it though most especially if your single entry . and you cannot stay 72days you can get 2 to 3 months as ryan mentioned its all visa officer's decision