Lauren had 49 stamps in the beginning. Since she gives Kristen 12 stamps, and Ethan 15 stamps, we can add both amounts to assume the total number of stamps she gave away. 15+12=27, so she gave away 27 stamps. Lauren was left with 22 stamps. We can add 22 to 27 to find out how many stamps she had in all. 27+22=49. Therefore, we can come to the conclusion that Lauren had 49 stamps at the start.
Hope this helps o(〃^▽^〃)o