`= (-12 + 13) + (-18+17)`
`= -1 + 1`
`= 0`.
`(-12) + 13 + (-18) + 17`
`= -12 + 13 - 18 + 17`
`=(-12-18) + (13 +17)`
`=-30 + 30`
`= 0 `
`-12 + 13 + -18 + 17`
`= (-12 - 18) + (13 + 17)`
`= -30 + 30`
`= 0`
(−12)+13+(−18)+17
=−12+13−18+17
=(−12−18)+(13+17)
=−30+30
=0