a) 19 . 43 + -20 . 43 - -40
= (19 + -20) . 43 + 40
= -1 . 43 + 40
= -43 + 40
= -3
b) 15 . -236 + 15 . 235
= 15 . (-236 + 235)
= 15 . -1
= -15
c) 237 . -28 + 28 . 137
= -237 . 28 + 28 . 137
= (-237 + 137) . 28
= -100 . 28
= -2800
d) 38 . (27 - 44) - 27 . (38 - 44)
= 38 . 27 - 38 . 44 - 27 . 38 - 27 . 44
= 38 . 27 - 27 . 38 - 38 . 44 + 27.44
= -38 . 44 + 27 . 44
= (-38 + 27) . 44
= -11 . 44
= -484