In Level 1, Session 29, the phrase "how long" is introduced as "quanto tempo." In Spanish, the preposition "por" is required to correctly form this construction: "¿Por cuánto tiempo queda aquí?" I was stricken that the lesson did not include the preposition in the construction of the Italian phrase. When I search phrases that use this construction on Italian websites, it seems that "per quanto tempo" is the most common way to express this phrase. Was the preposition left out in this Fluenz lesson because it is dropped colloquially, and we usually don't include it in English? Or are the websites that use the preposition "per" adding it improperly? Thanks!