What is 3(x+6x-3x-3x)?

For this, all you have to do is multiply the 3 to each individual term:

3*x = 3x

3*6x = 18x

3*-3x = -9x

3*-3x = -9x

 

Now, add up all the terms:

3x + 18x - 9x - 9x

 

It is easy to notice that we cancel out 18x with -9x - 9x since 18x - 18x = 0, leaving us with 3x.

 

3x is the final answer.