When the third and fourth digit of a four-digit number are reversed, the value changes
by *A*, when the second and third are reversed, the value changes by *B*, and
when the first and second are reversed, the value changes by *C*. For example, for
the number 2147, we have *A* = 27, *B* = 270, and *C* = −900.

For an arbitrary four-digit number, by how much does the value change when the first
and fourth digits are reversed? Please give your answer in terms of *A*, *B*,
and *C*.