a, x - 96 = (443 - x) - 15
<=>x - 96 = 443 - x - 15
<=>x + x = 443 - 15 + 96
<=>2x = 524
<=>x = 524 : 2
<=>x = 262
b, (x - 12) - 15 = (20 - 7) - (18 + x)
<=>x - 12 - 15 = 20 - 7 - 18 - x
<=>x + x = 20 - 7 - 18 + 12 + 15
<=>2x = 22
<=> x = 22 : 2
<=> x = 11