Alright for this you need these rules:
Group everything together
When isolating the variable do the opposite operation and do it on both sides.
You'll see what I mean
So for this it's 3x+4 = 2x-7x-9. So on the side with the -9 group the two variables together. Now you have -5x.
3x+4=-5x-9.
Now just subtract four from the side with 3x, as we are isolating the variable, and subtract it also from the other side, follow the rule. Now you have 3x=-5x-13. Next do what I did with the 4 and ADD 5x to each side, now you have 8x = 13. Divide each side to isolate even further and get x = 13/8.
Your final answer is:
x = 1 5/8