Each one of these answers is incorrect. state why the answer is incorrect, the correct answer, and what property of indices is used.

What subject is this?

The first one is correct
Second correct
third incorrect. 

Hope this helped

The first one is incorrect because (4x)^2 is the same as 4x^2 and not 8x^2.
2(4x)^2=8x^2 would however, be right.

The second one is incorrect because a number squared can never be negative as a negative* a negative is always a positive, a correct answer would be: 3^2=9

The third one is incorrect because 6/12=0.5 not 2, a correct answer would be:
12x^8/6x^4=2x^4

Hope this helps :)