This is the answer because like terms are alike. For example: With 2x and 5x what do they have in common? They have the x in common. Another example is if you have (2 + 7 + 5x + 10y). What are the like terms? 2 and 7, because they are both integers. Also, if you are trying to solve an expression such as the last example, then you would add 2 + 7, because they are similar, so they can be added. So it would be (9 + 5x + 10y).
