The sum of three numbers is 975. If you subtract x from each of these numbers you obtain 12, 345, and 126 respectively. What is x?

a + b + c = 975

a - x = 12
b - x = 345
c - x = 126
--------------add
a+b+c -3 x = 483
so
975 - 3 x = 483
3 x = 492
x = 164