I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "Each year, the southern California area has about 10,000 earthquakes. Nearly all of them are so small that they are not felt. Only several hundred are greater than magnitude 3.0, and only about 15–20 are greater than magnitude 4.0. The magnitude 6.7 1994 Northridge earthquake was particularly destructive, causing a substantial number of deaths, injuries, and structural collapses. It caused the most property damage of any earthquake in U.S. history, estimated at over $20 billion."? 

How high on the Richter Scale was the $20 billion earthquake?