You can put this solution on YOUR website!
Think of it this way.
If I have two apples and add three apples, how many apples will I have?
How about 2 CDs and add 3 CDs, how many CDs will I have?
How about two pet alligators and add three more pet alligators?
The variable x takes the place of whatever the thing is.
So if I have two things and add three things, I'll always get five things, no matter what the thing is.