a) (-2017)- (28- 2017)
= -2017 -28 +2017
= (-2017 +2017) -28
= 0 -28
= -28
b) (17-299) +(17-26+299)
=17 -229 +17 -25 +229
=(17 +17) -(229 +229) -25
=34 -0 -25
=9
c) - (269 -357) + (269 -357)
=-269 +357 +269 -357
=(-269 +269) +(357 -357)
= 0 +0 =0
d) (123 +345) + (456 -1230 - (2017 - (-345)))
=123 +345 +456 -1230 -2017 -345
=(345 -345) + (123 -1230) + (456 -2017)
=0 + (-1107) + (--1561)
= -2668