Final answer:
The enzyme that works backward and is necessary for DNA repair is endonuclease.
Step-by-step explanation:
The enzyme that works backward and is necessary for DNA repair is endonuclease. Endonuclease is involved in DNA repair mechanisms and is responsible for recognizing and cutting out damaged or incorrect bases in the DNA strand. It plays a crucial role in repairing DNA by removing the damaged section and allowing for the correct nucleotides to be inserted in its place.