First thing you must do when solving any math equation is read the question carefully taking note of all the numbers.
In this problem it is asking you to fish the arithmetic patters 23, 31, 39, 47.......
Usually to solve these kind of problems, you do the two first number minus each other:
23 - 31 = 8
Next, you would do the same with the next two numbers:
39 - 47 = 8
Now you can tell that there is a pattern going on here, for each number 8 is added.
So now we must to the math to find the next 3 numbers:
47 + 8 = 55
55 + 8 = 63
63 + 8 = 71
Thus, your three numbers 55, 63, and 71.
Just keep in mind that this way of solving does not work for all arithmetic patterns.
Hope this helped! :)