a) -15 + ( - 9 ) x ( - 4 + 5 ) - ( - 3 - 8 ) x ( - 7 + 3 ) = - 68
= - 15 + ( - 9 ) x ( + 1 ) - ( - 11 ) x ( - 4 ) =
= - 15 - 9 - 44 =
= - 24 - 44 =
= - 68
b) 23 - 5 x ( - 9 - 3 ) + ( 7 - 15) x ( - 2 - 4) = 131
= 23 - 5 x ( - 12 ) + ( - 8 ) x ( - 6 ) =
= 23 + 60 + 48 =
= 131
c) - 4 + ( - 6 - 9 ) x ( - 9 + 7 ) - ( 5 + 3 - 1 ) x ( - 4 + 3 ) = 33
= - 4 + ( - 15 ) x ( - 2) - ( + 7 ) x ( - 1) =
= - 4 + 30 + 7 =
= 26 + 7 =
= 33
