Math Foundation/DIVISIBILITY DRILL 7 QUESTION 28 & 29

[The MonicaA374]

I'm having problems understanding these two questions.

28. If 6 and 14 are factors of y, must y be divisible by 21?

29. If 7y is a multiple of of 210, must y be a multiple of 12?

[Sage Pearce-Higgins]

You may find the Foundations of Math Workshop I a useful resource to watch. However, in short, "divisible by 2" means the same as "has a '2' among its prime factors". We can apply the same idea to question 28 and say that, since 6 and 14 are factors of y, y must have a '2', a '3', and a '7' among its prime factors. Now, any number that has a '3', and a '7' among its prime factors is divisible by 21.

Also check out the Divisibility chapter in the Foundations of Math book.