Let \( C(\alpha, \beta) \) be the circumcenter of the triangle formed by the lines \( 4x + 3y = 69 \), \( 4y - 3x = 17 \) and \( x + 7y = 61 \). Then \( (\alpha - \beta)^2 + \alpha + \beta \) is equal to:
\( 16 \)
\( 17 \)
\( 18 \)
\( 15 \)