What is the answer and click pic to see the whole thing

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

Aline that intersects one of two parallel lines intersects the other also always sometimes never

Monitors manufactured by tsi electronics have life spans that have a normal distribution with a standard deviation of 1800 hours and a mean life span of 20,000 hours. if a monitor is selected at random, find the probability that the life span of the monitor will be more than 17,659 hours. round your answer to four decimal places.