a, 1125 : 3^2 + 4^3. 125- 125 : 5^2
= 1125 : 9 + 64 . 125- 125 : 25
= 125 + 8000 - 5
= 8120
b, 20 . 45 + 20 . 55
= 20 . ( 45+55 )
= 20 . 100
= 2000
c, 12 - ( 3^8 : 3^5 - 15 )
= 12 - ( 3^3 - 15)
= 12 - ( 27 - 15 )
= 12 - 12
= 0
d, ( 25 + 51 ) + ( 42 - 25 - 53 - 51)
= 25 + 51 + 42 - 25 - 53 - 51
= ( 25 - 25) + ( 51 - 51) + 42 - 53
= 0 + 0 + 42 - 53
= 42 - 53
= -11