If you're wondering why, the answer is very simple. You just have to look for key words. I saw the word "grow". If grow means to increase, and so does "add", then you will need to add.
You don't have any numbers in the question so this isn't possible to be answered. Feel free to add the numbers under this comment, if you still need help.
there were three times as many new subscribers in the 20-29 and the 30-39 age groups combined for the chronicle than in the 20-29 age group for the times.
