First you have to distribute the negative(=-1) with the numbers in the parentheses.
-1×9=-:
-1×-3x=3x
You now have:
4x-9+3x=8x-1
Now combine like terms:
4x+3x=7x
Now you have:
7x-9=8x-1
Now isolate that x:
7x-8x=-x
-1+9=8
You now have:
-x=8
Divide by -1 and get:
x=-8