How to solve? im doing piecewise functions

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

The boiling point of water at an elevation of 0 feet is 212 degrees fahrenheit (°f). for every 1,000 feet of increase in elevation, the boiling point of water decreases by about 2°f. which of the following represents this relationship if b is the boiling point of water at an elevation of e thousand feet? a) e = 2b - 212 b) b = 2e - 212 c) e = -2b + 212 d) b = -2e + 212

Which value of m will create a system of parallel lines with no solution? y= mx - 6 8x - 4y = 12