a. 72 + 56 + 28
= ( 72 + 28 ) + 56
= 100 + 56
= 156
b.27,145 - 27,44 - 27
= - 0 , 295 - 27
= - 27, 295
c. -9756 + (2015 + 9756)
= - 9756 + 9756 + 2015
= 0 + 2015
= 2015
d.160 - (23 . 52 - 9 . 52)
= 160 - ( 52 . ( 23 - 9 ))
= 160 - ( 52 . 0 )
= 160 - 0
= 160