I am not sure what exactly you are trying to find here, but we can write what you have written:

8 more than two times a number

As an function. The strategy for doing this is as follows:

Let's call this number X. We want to find what is two times this number, in other words 2X. Now, once we have twice this number, we want to find what 8 more of this number is. This would be adding 8 to 2X, in other words 2X + 8.

In the future, the word "times" gives you a clue that you will be multiplying, and the word "more" gives you a clue that you will be adding.