True, each number is getting doubled, both sides are proportionally staying the same.
Answer:
1,848
Step-by-step explanation:

First, lets take all the x values on one side.
3x + x + 8 = -x + x + 20
4x + 8 = 20
Now, lets put the numbers on the other side.
4x + 8 - 8 = 20 - 8
4x = 12
x = 3
Hope this helps!
<span />
Three and seventy-five hundredths.
Hope I helped! :P