I'm trying to recreate someone's data table in an academic paper to make sure I am doing this right, but I am having a really tough time with it. In radiocarbon dating on bone, if the owner of the bone has been eating fish, it will cause something called a marine reservoir effect that needs to be corrected for. In order to correct, we use linear interpolation between the end points -21 (representing a 100% non-fish diet - parts per million of carbon isotopes) and -12.5 (representing a 100% fish diet). I know the values for each bone between those two numbers (e.g., -20.1, -16.5), and I need to figure out the percentage of marine diet that each bone has. The original table I'm trying to recreate is here: https://journals.uair.arizona.edu/index.php/radiocarbon/article/viewFile/3805/3230 (Table 1).

Any help at all would be very much appreciated.