a. -34 + 16 + 34 + 7
= [ ( -34 ) + 34 ] + ( 16 + 7 )
= 0 + 23
= 23
b. 17 + ( -35 ) + ( - 37 ) + 35
= [ ( -35 ) + 35 ] + [ ( -37) + 17 ]
= 0 + ( -20 )
= ( -20 )
c. 3157 + 57 - 3159 - 66
( 3157 - 3159 ) + ( 57 - 66 )
= (-2) + ( -9 )
= (-11)
d. 8715 + (-1250) + 56 - 250
7465 + 56 - 250
= 7521 - 250
= 7271