How much does it cost to rent an office in the Willis Tower?
Rents average $24 a foot at skyscraper, with United occupying 20% of office space.
Did the Willis Tower collapse?
It was designed to withstand the impact of a jet, but both its towers collapsed this morning after planes rammed them. The structural engineer who designed the towers said as recently as last week that their steel columns could remain standing if they were hit by a 707.