423+12*x=507
12x = 507 - 423
12x = 84
x = 84 : 12
x = 7
448:(123-x)=8
123 - x = 448 : 8
123 - x = 56
x = 123 - 56
x = 67
423+12*x=507
12x = 507 - 423
12x = 84
x = 84 : 12
x = 7
448:(123-x)=8
123 - x = 448 : 8
123 - x = 56
x = 123 - 56
x = 67
12*x=84
X=84/12
X=7