a, 15 + 23 + ( -25 ) + ( -23 )
= 15 + 23 - 25 - 23
= ( 15 - 25 ) + ( 23 - 23 )
= -10
b, 125 + 4 . [ ( -5 ) . 2 + 20 ]
= 125 + 4 . [ -10 + 20 ]
= 125 + 4 . 10
= 125 + 40
= 165
c, 49 . ( -23 ) + 23 . ( -51 )
= ( -49 ) . 23 + 23 . ( -51 )
= 23 . ( -100 )
= -2300
d, 2155 - ( 174 + 2155 )
= 2155 - 174 - 2155
= ( 2155 - 2155 ) - 174
= 0 - 174
= -174