Answer: 8
So, the first approach with this problem you should take is writing out the mathematical expression in association to what is being described.
To help break down the statement, let's look over it "twice a number (i.e., the number we are looking for multiplied by 2), decreased by 4 (subtraction), is at least 12 (equals that value).
Therefore,
2(x) - 4 = 12
Using algebra to isolate the x variable, we find that:
x = 8
I hope that I understood what was being asked enough to help!