a) 20- ( -40 ) +10 b) - 21+ ( -13 ) -4
= ( 40+ 20 ) +10 = - ( 21+13 )- 4
= 60+ 10 = ( -34 ) - 4
= 70 = - ( 34+ 4 )
= - 38
c) ( 3-23 ) - ( 4- 10 ) d) ( -8 + 15 ) - ( -6-20)
= ( - 20 ) - ( -6 ) = 7+ - 26
= - ( 20+ 6 ) = -19
= - 26
b: =-21-13-4=-34-4=-38
d: =-8+15+6+20=7+6+20=33