Hi there! 
We have:
-3 - x = -2w + 4v 
Solve for x 
Start by adding 3 to both sides 
-3 - x + 3 = -2w + 4v + 3 
-x = -2w + 4v + 3 
Remember that we cannot leave the x with a negative sign. 
There are two ways to remove the negative sign. 
1) We can divide both sides by -1 
2) We can multiply both sides by -1 
In this, I am going to multiply both sides by -1 
-x * -1 = (-2w + 4v + 3)(-1)
x = 2w - 4v - 3 
I hope this helps. 
Please let me know if you have questions about the answer. 
Thanks!