a, ( 35 +75 ) + ( 345 - 35 -75 )
= 35 + 75 + 345 - 35 - 75
= 35 - 35 + 75 - 75 + 345
= 0 + 0 + 345
= 345
b, -(515-80+91)-(2003+80-91)
= - 515 + 80 - 91 - 2003 - 80 + 91
= - 515 - 2003
= - 2518
c,25-(-17)+24-12
= 25 - 17 + 24 - 12
= 8 + 24 - 12
= 32 - 12
= 20
d,235-(34+135)-100
= 235 - 34 - 135 - 100
= 235 - 135 - 34 - 100
= 100 - 34 - 100
= - 34