Figure 21 shows Minot International Airport (MOT) surrounded by a dashed blue line with a boxed number "42" near it. What does the boxed number represent?

Why: FAA-CT-8080-2H Legend 1 defines a boxed number as the "Ceiling of Class D Airspace in hundreds of feet," adding that a *minus* ceiling value would mean surface up to but not including that value. The plain "42" near Minot's dashed blue Class D boundary therefore means the Class D airspace there has a ceiling of 4,200 feet MSL.

• Misreads the boxed Class D ceiling figure as a frequency; chart frequencies are written in MHz next to a "CT" or similar label, not inside a boxed number next to the airspace boundary.
• Invents a meaning for the boxed number that Legend 1 does not support — the box specifically denotes a Class D ceiling, not an approach-procedure count.