a) 12 - (7 + 12) + 2017
= 12 - 7 - 12 + 2017
= (12 - 12) + (2017 - 7)
= 0 + 2010
= 2010
b) (2018 - 29) - (237 + 2018)
= 2018 - 29 - 237 - 2018
= (2018 - 2018) + (-29 - 237)
= 0 - 266
= -266
c) 569 - (12 - 569) + 12
= 569 - 12 + 569 + 12
= (569 + 569) + (12 - 12)
= 1138 + 0
= 1138