Question 1) The train arrives every 8 minutes so what you want to do is draw a timeline, like you have done, and go up in gaps of 8 minutes.
10:04, 10:12, 10:20, 10:28, 10:36, 10:44, 10:52, 11:00, 11:08, 11:16.
If you finish at 11:15 and the next train gets there at 11:16, the next train that you can take will arrive in 1 minute.
Question 2) As she wants all the displays to have the same number in each row (to have the same number of columns) you are going to want to find the GCF of 9, 12 and 21. The largest factor of all 3 numbers is 3 therefore each row will have 3 tokens in it.
9 = 3 columns x 3 rows
12 = 3 columns x 4 rows
21 = 3 columns x 7 rows
A prime number is a number that's factors are only one and itself.
A composite number is a number that has additional factors other than one and itself.
As 9, 12 and 21 can all be divided by 3, they must be Composite numbers
