Which of the following has a value of 8 squared by 4?

8 squared over 4 = 64/4 = 16
What I believe you're asking is:

8 = 4/x

If that's right, then x would have to be .5, because 4 / .5 = 4 x 2 = 8.
If that's not what you mean, you would have to re-Word the question in the right way, which I cannot help with because I do not know what you mean, then.
Also, either way, I do not believe this belongs in the Roman Numerals section. This would belong in either general math or simple division.