I don't see any answers provided so, i'm going to add, subtract, multiply, and divide with 6 and -6.
6 + -6 = 0 | Another solution: Any number multiplied by 0
6 - (-6) = 12 | Another Solution: 6 + 6
6 · -6 = -36 | Another Solution: -6 squared
6 / -6 = -1 | Another Solution: -1 x 1