How is this true?

6x^3 + 2x^2 -x + 1 = -x^2 +2x + 1 in F (sub3) [x]

There is a dash over the 6, 2, 1 in the first polynomial and a dash over the 2, 1 in the second

I'm thinking original algebra days and obviously thats not what were doing here. Can anyone explain how to figure the above.