6x + 3x = 9x
The reason is because 6x and 3x are like terms. They both have the same variable and the variable has the same degree of 1. That means you can add 6x and 3x.
If you factor out x, you get:
6x + 3x = x(6+3)
Now, if we add 6 + 3, we get 9.
x(6+3) = x(9) = 9x
Therefore, 6x + 3x = 9x.
