For a 35 pounds suitcase, the airline charges $0 for the first 20 pounds and $2 per pound for the remaining 15 pounds as the airline charges for only pounds over 20
This is because she has a 1/6 chance of getting a 3 on the first try and then a 1/2 chance of getting an even on the second. Multiply these two together to get your answer.
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.