1a) Beware of the dangerous, deep hole ahead.
=> the hole is both dangerous and deep. Note that, the comma represents an omitted conjunction: the dangerous and deep hole ahead.
1b) Beware of the dangerously deep hole ahead.
=> the depth of the hole is dangerous. The adverb dangerously modifies the adjective deep.
Most people estimate between 40 and 60 miles and [they] are correct [in their estimation]. 3) Extract means to draw or pull out, and when it refers to removing something for separate consideration or publication it's synonymous with excerpt.