a, 234 - [ ( - 45 ) - ( 234) + 65 ]
= 234 - [ -280+65]
=234 - (-215)
= 449
b, - 25 . 21 + 25 . 72 + 49 . 25
=-25 x 72 + 25 .21 - 49 x 25
=25 x -72 + 25 . 21 - 49 . 25
=25 x (-72 + 21 - 49)
=25 x -100
=-2500
27.(15-12)-15.(27-12)
= 27.15 - 27.12 - 15.27 - 15.12
= (27.15-15.27) - 12.(27-12)
= 0 - 12.15
= 180