Our lecturer split it into
Institution: bei der, beim
Haus/Gebäude: im, in dem
But I mix things up.
- How can "in Büro" be correct (is it a Stadt?)?
- Can anyone give a concise guide, reference or article about it?
P.S.: I do understand, that in this case we use dative and their gender forms are dem/der/dem/den correspondingly.