Dynamic Programming Example: Solution is given. I'm looking for an explanantion that will help me understand the process in getting the answer! Thanks!

17) Dynamic programming, popular for sequence alignment, can also be used for spell checking Assuming that a match is worth 10, a mismatch is worth 5, and a gap "costs" -5, which of these four words is closest to the word "graffe" typed by a user? Write the score of the optimal alignment next to each word (gaps at the start or at the end do not count). A) gaff B) graft C) grail D) giraffe best score: 40-5 35 best score: 40+5 45 best score: 30+5+5 = 40 best score: 60-5-55