Consider 13(mod 6) and 20(mod 6). Which of the following is true?
a. 13(mod 6) and 20(mod 6) are in the same equivalence class.
b. 13(mod 6) = 20(mod 6)
c. 13(mod 6) + 20(mod 6) = 3
d. 13(mod 6) + 20(mod 6) = 1