#2 is x = 16
[Given]
20 + x = 4 + 2x
[Subtract x from both sides]
20 = 4 + x
[Subtract 4 from both sides]
16 = x
#3 is x = 4
[Given]
12x - 16 = 8 + 6x
[Add 16 to both sides]
12x = 24 + 6x
[Subtract 6x from both sides]
6x = 24
[Divide both sides by 6]
x = 4
Note
With the of "add 16" or "subtract x" you can flip the order. If you have multiply variables on each side you can pick the steps you take. I usually, when possible, like to make it so I end up with all negative or all positive numbers because it is easier for me!
Have a nice day!
I hope this is what you are looking for, but if not - comment! I will edit and update my answer accordingly. (ノ^∇^)
- Heather