a)
531-6*x=453
6*x = 531 - 453
6*x = 78
x = 78:6
x = 13
b)
14*×-15=13
14*x = 13+15
14*x = 28
x = 28 : 14
x = 2
c)
12.435*(2*x-8)=0
2*x - 8 = 0
2*x = 8
x = 8 : 2
x = 4
d)
512:(x+9)=18
x + 9 = 512 : 18
x + 9 = 512/18
x = 512/18 - 9
x = 256/9 - 9
x = (256-9×9)/9
x = (256 - 81)/9
x = 175/9