`1.` When did you work in London ?

`-` How long + have/has + S + Vpp + ... ?

`=` When + did + S + V-inf + ... ?

`2.` He has his car washed twice a month.

`-` ask sb to V-inf : yêu cầu ai làm gì

`-` have sth done : nhờ ai làm gì

`1,` How long have you worked in London?

`⇒` When did you work in London ?

`-` When + did + S + Vbare + O?

`Trans:` Bạn làm việc ở London khi nào ?

`2,` He asks someone to wash his car twice a month

`⇒` He has his car washed twice a month

`-` Have sth done : nhờ ai đó làm gì?

______________________

`Shyanki`