Answer:
-7
Explanation:
Equation: 2x - 4 = -18
First, add 4 to both sides: 
2x = -14
Finally, divide both sides by 2: 
x = -7
Check (optional): 
2(-7) - 4 = -18
-14 - 4 = -18
-18 = -18 so this is correct
If you're confused about any of these steps, just let me know and I'll try to clear it up for you! :)