b)315+(125-x)=435
125-x=435-315
125-x=120
x=125-120
x=5
a) 575 - ( 6x + 70 ) = 447
( 6x + 70 ) = 575 - 447
( 6x - 70 ) = 128
6x = 128 + 70
6x = 198
x = 198 : 6
x = 33
b) 315 + ( 125 - x ) = 435
( 125 - x ) = 435 - 315
125 - x = 120
x = 125 - 120
x = 5