Hel p plz plz

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

Elena and her husband marc both drive to work. elena's car has a current mileage (total distance driven) of 15,000 and she drives 23,000 miles more each year. marc's car has a current mileage of 46,000 and he drives 9,000 miles more each year. will the mileages for the two cars ever be equal? explain.

Question: what is the value of x 4x-2= (-7) +5x. it would be greatly appreciated if someone could actually explain to me step by step