[IMGCAP(1)] The bottom flag gives a clue as to the group that has offices inside these glass walls northwest of the Capitol. But if that’s not enough of a hint, the surroundings reflected in the wall might help, too. Check back next week for the answer. [IMGCAP(2)] Last time, we challenged you to figure out where the plane shown below was on display. The Air and Space Museum would have been way too obvious. In fact, it’s hanging at the National Postal Museum near Union Station.