By factoring what is 3c squared minus 17c minus 6?

3c^(2) -17c - 6

Factors to

( 3c + 1)(c - 6 )

NB When you apply FOIL to the bracketed terms.

F ; 3c X c = 3c^(2)

O ; 3c X -6 = -18c

I ; 1 X c = c

L ; 1 x -6 = -6

Collecting 'like' terms

3c^(2) - 18c + c - 6

3c^(2) - 17c - 6 ( As before).