cool, thank you!
so, 'mari kita makan di restoran itu di situ' you would say among friends about the restaurant you can see that's say just across the road...
while, 'mari kita makan di restoran itu di sana' you would say in less casual company and/ or about a restaurant that's say a few blocks or more away...
yes I tried this also. I suppose it is simply not complete. However the english 'there' ambiguous. It could refere to both a place (as in: it is there) and a destination (e.g. i want to go there). The place would be translated as di sana as accepted in this exercise, where the destination would be ke sana. Not knowing which was meant I thought 'sana' alone would do the trick. But we are learning to make complete expressions here, that's my takeaway.