17-crabon had two natural stable isotopes: 12c and 13c

write the delta notation for how one would calculate fractionation of the heavier isotope.
pretend you collected a coral fossil with 0.011 g of 13c per 1 g of 12c. using the pbd standard) pee dee belemnite, a fossil with 0.0112372 g 13c for every 1g 12c), what is the δ 13c?
is your answer from "b" negative or positive, and what does it mean about 13c in this case?