a) 15 x 12 - 3 x 5 x 10
= 15 x 12 - 15 x 10
= 15 x (12 - 10)
= 15 x 2
= 30
C2 : 15 x 12 - 3 x 5 x 10
= 180 - 150
= 30
b) 45 - 9 x (13 + 5)
= 45 - 9 x 18
= 9 x 5 - 9 x 18
= 9 x (5 - 18)
= 9 x (-13)
= -117
c) 29 x (19 - 13) - 19 x (29 - 13)
= 29 x 6 - 19 x 16
= 174 - 304
= -130