How do i solve this problem using the substitution method?

What is the greatest common factor of 8 and 36

Which of the following points is collinear with (-2,1) and (0,3)

How many of the 250 grandparents in the population would you expect to prefer online shopping with merchant a? merchant a: 4 merchant b: 6 merchant c: 2 merchant d: 3 other: 5 none: 5 answer choices: a.about 4 b.about 8 c.about 40 d.about 21