Translation:He has sent a machine in his place.
If it's not accepted it should be.
I thought that the sentence was very simple except that there is no indication as to who sent the machine in his place. "You (formal) sent the machine in your place" , "You (formal) sent the machine in his place", "He sent the machine in his place". I understand that "Someone sent a machine in place of (instead of, to take the place of) someone else. Duolong however rejected my answer "He sent the machine in his place (in place of him)"
I too love this program but it does come up with some strange and funny sentences. I don't know if you've seen any of the morbid sentences this program dreams up from time to time. Something about a body in the living room and things like that. Real creepy. I just hope that I never have to actually know how to say that to someone.
No, the fact that 'machine' is feminine doesn't affect the gender of pronouns that refer to other people or things. Duolingo accepts either 'his' or 'her' for the 'su' in this sentence, but not 'your'. It is perfectly correct to use 'su' for 'your' if you are speaking formally to one person. I will report this as an error.
Hola Caversham: Maybe "in his stead" is British (?) and Duo maybe only accepts American (?) Just a thought -- I have no inside information about Duolingo. I am USAmerican and I have never said "in his stead". But you would have to ask Duo directly on "Report a Problem" to get them to accept it.
Oh, I think the main problem is that your sentence is not in the perfect tense but in the simple past. Ha enviado = has sent and not simply sent. So you could say "He has sent a machine in its place." and that should be accepted (whether it's in their database or not, I don't know).
Su = de usted and tu = de ti (the tú form). It's just a matter of if you are using the formal you for the person your talking to or not. So you would basically use su if you're talking to a stranger, someone older than you, or someone you respect, and tu for a family member, friend, or child.
You could defenitely take some lessons from Fluencia,I know many that have qiut your coarse because you make each lesson much harder than is necessary.Most people take this coarse to learn enough spanish to get by not to perfect it.Most of your sentences aren`t even used where we are[Ecuador]