Well, to simply this expression, you would follow the Order of Operations, which is
1) Parenthesis
2) Exponents
3) Multiply OR Divide from right to left
4) Add OR Subtract from right to left
Since there are no Parenthesis, you'd move to Exponents as we have one of those, so doing 6^2 is your first step, which is choice A.
So, A is your answer.
Hope this helps,
Brian