Answer:
12x - 5
Explanation:
3x + 9x - 5 can be easily simplified by combining like terms.
3x and 9x are like terms because they both contain the same variable and the same exponent (understood to be 1).
Therefore, because an addition sign separates the two terms, it is expected of you to add the two together. To do this, just add the terms together as you would any other terms.
3x + 9x = 12x
Because the 5 is the only constant in the equation, it cannot be combined with anything else.
The simplified expression is 12x - 5.