Robert stands atop a 1,380-foot hill. he climbs down, reaching the bottom of the hill in 30 minutes. what is robert’s average rate of elevation change in feet per minute?

This is an equation of elevation change.  Since it takes 30 minutes do go down 1380 feet, or undergo an elevation change of -1380 feet, the answer is -1380/30, or an average elevation change of -46 feet per minute

Yes, two vertical lines can be complementary