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.