Making a list can help you solve a math problem because it shows you the information you will be using.
Sally is 13 years old. Sally's brother Mark is twice as old as Sally. Sally's older sister Daffy is the sum of Sally and Mark's age. How old is Daffy?
making a list in this question tells you all of the different ages and lists them out in a row.
1. You already did it.
2. Table
3. t (years since 1990)
4. n (# of cigarettes sold)
5. (t, n)
6. You can see the distribution of the data pretty neatly. There are also many more advantages including it's easier to calculate standard deviation, easier to see the mean, mode and median, and it's also much easier to just tell the extrema of the dataset by just looking at the scattergram.
Answer:
35
Step-by-step explanation:

Solving this ^^ would equal t=35.
To answer this question I tried to find a common multiple of 21 and 35 which I found to be 105. As they are in minutes 105 is 1 hour and 45 minutes; after this I found 1 hour 45 munutes after 7:30, I then got 9:15
9:15 is my answer