Whenever you have something to the negative power, it will result in a fraction. So, if you have seven to the second power, it would be 49, and then you turn that into a fraction, which would be 1/49.
Since the exponent 2 is negative, you will need to make it positive first. In order to do so, you can put 7^2 in the denominator. (If the original question was 1/7^-2 you could put 7^2 in the numerator to cancel out the negative). By doing this, the negative is removed and you are able to answer the question as 1/7^2 . The answer would then be D, since 7^2 is 49, but you put the number in the denominator because of the negative exponent.
I hope this makes sense!
(also: I am not exactly positive as to what standard form would be with just one number and an exponent, so I answered this as I have learned in my math classes.)
