The number doing the dividing in a division problem

What is the missing reason in step 5? linear pair postulategivendefinition of complementary anglescongruent complements theorem

An airport in death valley is 60 feet below sea level, and an airplane is flying 2,000 feet above sea level. how many feet must the plane descend in order to land? a. 2060 b. 2000 feet c. 1940 feet d. 1880 feet e.1400 feet will mark as brainliest

What is r i 4.5+10r=-6.5 with work pls