How to know that in which method should i factorise?

Add the two expressions 3.8b - 7 and 2.9b + 9 enter your answer in simplified form

2people are trying different phones to see which one has the better talk time. chatlong has an average of 18 hours with a standard deviation of 2 hours and talk-a-lot has an average of 20 hours with a standard deviation of 3. the two people who tested their phones both got 20 hours of use on their phones. for the z-scores i got 1 for the chatlong company and 0 for talk-a-lot. what is the percentile for each z-score?

Aline passes through 3,7 and 6,9 what equation represents the line