Negative exponents work like this:

So, in order to evaluate a negative exponent, you simply have to invert the base, and then raise to the positive equivalent of the exponent.
As an example, here are the first three exercises:



You can work out the rest applying this logic.
P(sum = 6) = 5/36 ; P(sum = 12) = 1/36
expected payoff = (5/36)(5) + (1/36)(9) = $0.94
the 2nd expression is the answer