If the roll was 66 1/2 rolls long, we have to calculate and know how many pieces of wrapping paper for the roll so if each wrapping paper is 9 1/2 then you would have to divide 66 1/2 by 9 1/2 so you would need 7 wrapping papers.
Your answer is because the numbers raised to negative powers must be flipped over the divisor to become positive. Then, when multiplying 2 and z, you add their exponents.